See.. if you would have told us this from the beginning, you would have been done by now..
Your problem is with mysql, not the installation of gts
Now, have you prepared mysql?
try running these:
sudo mysql_install_db --user=mysql
I'm not sure about the mysql user in centos.. But I think it is 'mysql'...
If all goes well, run afterwards:
Do not confuse the 'root' user of mysql with the 'root' system user
sudo service mysqld start
According to the documentation of Gts you will at some point (4.1 Initializing the SQL Database Tables) need to know the root user and password of you mysql database