Fix "Centos" to official notation "CentOS".
Fix "Centos" to official notation "CentOS".

Change-Id: I2f76fe3a19cd2ebf004d0a7c14852f20f3dadd9e

noironetworks/devstack,group-policy/devstack,group-policy/devstack,noironetworks/devstack,openstack-dev/devstack,openstack-dev/devstack,dtroyer/devstack,nawawi/openstack,dtroyer/devstack,nawawi/openstack