I find having lots of references to IPV6 addresses a little distracting, especially as at this point in time I am not using them, there is however a really easy way to disable IPV6 in CentOS (and you don't have to remove any IPV6 reference from the ifcfg-xxxx files).
Edit the /etc/sysctl.conf
Enter the following to disbale IPV6 on ALL interfaces:
net.ipv6.conf.all.disable_ipv6 = 1
Alternatively you can disable IPV6 on specific interfaces by using: (assuming en016777736 is the interface name)
net.ipv6.conf.eno16777736.disable_ipv6 = 1
Now enter sysctl -p or reboot, thats it.