[stack@localhost ~]$ sudo cp CentOS-7-x86_64-GenericCloud.qcow2 /var/lib/libvirt/images/undercloud.qcow2
[stack@localhost ~]$ sudo qemu-img resize /var/lib/libvirt/images/undercloud.qcow2 +120G
Image resized.
[stack@localhost ~]$

[stack@localhost ~]$
[stack@localhost ~]$ sudo virt-customize -v -x -a /var/lib/libvirt/images/undercloud.qcow2 --run-command 'echo -e "d\nn\n\n\n\n\nw\n" | fdisk /dev/sda'
[ 0.0] Examining the guest ...
libguestfs: trace: set_verbose true
libguestfs: trace: set_verbose = 0
libguestfs: trace: set_network true
libguestfs: trace: set_network = 0
libguestfs: trace: add_drive "/var/lib/libvirt/images/undercloud.qcow2" "readonly:false" "protocol:file" "discard:besteffort"
libguestfs: trace: add_drive = 0
libguestfs: trace: launch
libguestfs: trace: get_tmpdir
libguestfs: trace: get_tmpdir = "/tmp" libguestfs: trace: version libguestfs: trace: version = libguestfs: trace: get_backend
libguestfs: trace: get_backend = "libvirt"
libguestfs: launch: program=virt-customize
libguestfs: launch: version=1.36.3rhel=7,release=6.el7_4.3,libvirt
libguestfs: launch: backend registered: unix
libguestfs: launch: backend registered: uml
libguestfs: launch: backend registered: libvirt
libguestfs: launch: backend registered: direct
libguestfs: launch: backend=libvirt
libguestfs: launch: tmpdir=/tmp/libguestfsWcfOGQ
libguestfs: launch: umask=0022
libguestfs: launch: euid=0
libguestfs: libvirt version = 3002000 (3.2.0)
libguestfs: guest random name = guestfs-5jx0vkvril0zvznw
libguestfs: connect to libvirt
libguestfs: opening libvirt handle: URI = qemu:///system, auth = default+wrapper, flags = 0 libguestfs: successfully opened libvirt handle: conn = 0x17c61c0
libguestfs: qemu version (reported by libvirt) = 1005003 (1.5.3)
libguestfs: get libvirt capabilities
libguestfs: parsing capabilities XML
libguestfs: trace: get_backend_setting "force_tcg"
libguestfs: trace: get_backend_setting = NULL (error)
libguestfs: trace: get_backend_setting "internal_libvirt_label"
libguestfs: trace: get_backend_setting = NULL (error)
libguestfs: trace: get_backend_setting "internal_libvirt_imagelabel"
libguestfs: trace: get_backend_setting = NULL (error)
libguestfs: trace: get_backend_setting "internal_libvirt_norelabel_disks"
libguestfs: trace: get_backend_setting = NULL (error)
libguestfs: build appliance
libguestfs: trace: get_cachedir
libguestfs: trace: get_cachedir = "/var/tmp"
libguestfs: begin building supermin appliance
libguestfs: run supermin
libguestfs: command: run: /usr/bin/supermin5
libguestfs: command: run: \ --build
libguestfs: command: run: \ --verbose
libguestfs: command: run: \ --if-newer
libguestfs: command: run: \ --lock /var/tmp/.guestfs-0/lock
libguestfs: command: run: \ --copy-kernel
libguestfs: command: run: \ -f ext2
libguestfs: command: run: \ --host-cpu x86_64
libguestfs: command: run: \ /usr/lib64/guestfs/supermin.d
libguestfs: command: run: \ -o /var/tmp/.guestfs-0/appliance.d
supermin: version: 5.1.16
supermin: rpm: detected RPM version 4.11
supermin: package handler: fedora/rpm
supermin: acquiring lock on /var/tmp/.guestfs-0/lock
supermin: if-newer: output does not need rebuilding
libguestfs: finished building supermin appliance
libguestfs: trace: disk_create "/tmp/libguestfsWcfOGQ/overlay1" "qcow2" -1 "backingfile:/var/tmp/.guestfs-0/appliance.d/root" "backingformat:raw"
libguestfs: command: run: qemu-img
libguestfs: command: run: \ create
libguestfs: command: run: \ -f qcow2
libguestfs: command: run: \ -o backing_file=/var/tmp/.guestfs-0/appliance.d/root,backing_fmt=raw
libguestfs: command: run: \ /tmp/libguestfsWcfOGQ/overlay1
Formatting '/tmp/libguestfsWcfOGQ/overlay1', fmt=qcow2 size=4294967296 backing_file='/var/tmp/.guestfs-0/appliance.d/root' backing_fmt='raw' encryption=off cluster_size=65536 lazy_refcounts=off
libguestfs: trace: disk_create = 0
libguestfs: trace: get_sockdir
libguestfs: trace: get_sockdir = "/tmp"
libguestfs: create libvirt XML
libguestfs: trace: disk_format "/var/lib/libvirt/images/undercloud.qcow2"
libguestfs: command: run: qemu-img
libguestfs: command: run: \ info
libguestfs: command: run: \ --output json
libguestfs: command: run: \ /dev/fd/9
libguestfs: parse_json: qemu-img info JSON output:\n{\n "virtual-size": 137438953472, \n "filename": "/dev/fd/9", \n "cluster-size": 65536, \n "format": "qcow2", \n "actual-size": 870076416, \n "format-specific": {\n "type": "qcow2", \n "data": {\n "compat": "0.10"\n }\n }, \n "dirty-flag": false\n}\n\n
libguestfs: trace: disk_format = "qcow2"
libguestfs: trace: get_cachedir
libguestfs: trace: get_cachedir = "/var/tmp"
libguestfs: libvirt XML:\n\n\n guestfs-5jx0vkvril0zvznw\n 500\n 500\n \n \n \n 1\n \n \n \n \n \n \n hvm\n /var/tmp/.guestfs-0/appliance.d/kernel\n /var/tmp/.guestfs-0/appliance.d/initrd\n panic=1 console=ttyS0 edd=off udevtimeout=6000 udev.event-timeout=6000 no_timer_check printk.time=1 cgroup_disable=memory usbcore.nousb cryptomgr.notests tsc=reliable 8250.nr_uarts=1 root=/dev/sdb selinux=0 guestfs_verbose=1 guestfs_network=1 TERM=xterm-256color\n \n \n destroy\n \n \n /dev/urandom\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n\n
libguestfs: trace: get_cachedir
libguestfs: trace: get_cachedir = "/var/tmp"
libguestfs: command: run: ls
libguestfs: command: run: \ -a
libguestfs: command: run: \ -l
libguestfs: command: run: \ -R
libguestfs: command: run: \ -Z /var/tmp/.guestfs-0
libguestfs: /var/tmp/.guestfs-0:
libguestfs: drwxr-xr-x. root root unconfined_u:object_r:user_tmp_t:s0 .
libguestfs: drwxrwxrwt. root root system_u:object_r:tmp_t:s0 ..
libguestfs: drwxr-xr-x. root root unconfined_u:object_r:user_tmp_t:s0 appliance.d
libguestfs: -rw-r--r--. root root unconfined_u:object_r:user_tmp_t:s0 lock
libguestfs:
libguestfs: /var/tmp/.guestfs-0/appliance.d:
libguestfs: drwxr-xr-x. root root unconfined_u:object_r:user_tmp_t:s0 .
libguestfs: drwxr-xr-x. root root unconfined_u:object_r:user_tmp_t:s0 ..
libguestfs: -rw-r--r--. qemu qemu system_u:object_r:virt_content_t:s0 initrd
libguestfs: -rwxr-xr-x. qemu qemu system_u:object_r:virt_content_t:s0 kernel
libguestfs: -rw-r--r--. qemu qemu system_u:object_r:virt_content_t:s0 root
libguestfs: command: run: ls
libguestfs: command: run: \ -a
libguestfs: command: run: \ -l
libguestfs: command: run: \ -Z /tmp/libguestfsGVhH0h
libguestfs: drwxr-xr-x. root root unconfined_u:object_r:user_tmp_t:s0 .
libguestfs: drwxrwxrwt. root root system_u:object_r:tmp_t:s0 ..
libguestfs: srw-rw----. root qemu unconfined_u:object_r:user_tmp_t:s0 console.sock
libguestfs: srw-rw----. root qemu unconfined_u:object_r:user_tmp_t:s0 guestfsd.sock
libguestfs: launch libvirt guest
libguestfs: trace: launch = -1 (error)
virt-customize: error: libguestfs error: could not create appliance through libvirt.

Try running qemu directly without libvirt using this environment variable: export LIBGUESTFS_BACKEND=direct

Original error from libvirt: internal error: process exited while connecting to monitor: failed to initialize KVM: Device or resource busy [code=1 int1=-1]
libguestfs: trace: close
libguestfs: closing guestfs handle 0x17c5870 (state 0)
libguestfs: command: run: rm
libguestfs: command: run: \ -rf /tmp/libguestfsWcfOGQ
libguestfs: command: run: rm
libguestfs: command: run: \ -rf /tmp/libguestfsGVhH0h
[stack@localhost ~]$
[stack@localhost ~]$