Turn docker3 into a CentOS 7 VM.
Add another CentOS 7 VM.
Change dockermonitor's IP address so it doesn't collide with docker4's IP address.
Reduce the RAM amounts.
Added a node definition for docker4.local.
Be more specific about which OS versions the nodes are.
Disable EPEL when installing Puppet so that we get Puppet from the official Puppet Labs repository.