Make centos seven great again
CentOS no longer comes configured as a server operating system. For example, NetworkManager and wpa_supplicant have no place on a server that is going to be connected to a single set of networks for its entire life. So let's make it great again.
Fix networking
Rename the network devices to something sane like eth0 and (if you have more) eth1, etc.
Update /etc/default/grub and add net.ifnames=0 to the kernel options. This tells the kernel to expose eth0 instead of eno2304923409 or whatever number it pulls out of its ass.
After you edit /etc/default/grub, rebuild the config with grub2-mkconfig -o /boot/grub2/grub.cfg. Without rebuilding the config, the kernel will never know it's not supposed to use the stupid ifnames. That makes the kernel very sad.
If you have a 70-persistent-net.rules file under /etc/udev/rules.d/, blow it away so udev doesn't shit itself on next boot.
Next, head over to /etc/sysconfig/network-scripts and move the ifcfg files to their new names (e.g. the first network device goes from ifcfg-enoXXXXXXX to ifcfg-eth0.) Once they're renamed crack those open with $editor and fix names in exactly the same way. Double check your changes, because if they're wrong, you won't have network on the next boot.
Package switcheroo
Remove some unnecessary packages with yum remove NetworkManager wpa_supplicant polkit and install some useful packages with yum install iptables-services epel-release.
Fix hostname
echo whateveryouwant.jpg > /etc/hostname then update your /etc/hosts file with your new hostname.
CentOS 7 is now usable
You should reboot so all the changes we made apply all at once. If you did something wrong, your system will probably be broken. If your system is broken, go rtfm.
Congratulations, CentOS is great again.