Investigate how Vagrant adapts libvirt instances to its environment and how to replace instance in node with another instance
Investigate how Vagrant creates libvirt instances.
Look for .vagrant directory in CONFIG and find out how vagrant defines libvirt instance in its environment.
Generate config (attached file to this issue) in CONFIG. So you will have two nodes with ubuntu and centos.
Then after investigation try to replace node0 with node1 and node1 with node0. So before replacement you had ubuntu at node0 and centos at node1 (check it with ssh) and after you should have centos at node0 and ubuntu at node1 (check it with ssh).
As a result after generating config from attached file and replacing its nodes with each other, check that you have centos on node0 and ubuntu on node1 with ssh (to check linux distro type http://www.cyberciti.biz/faq/find-linux-distribution-name-version-number/) and describe how to replace libvirt nodes in Vagrant environment in wiki(in Vagrant section create new section 'How to replace libvirt nodes').