BZ #1101077 - Improve check for all nodes to join cluster

https://bugzilla.redhat.com/show_bug.cgi?id=1101077

Improve the check we are using to make sure all nodes have cleanly
joined cluster before continuing to add fencing, thus making sure that
a node doesn't get prematurely fenced.
Merge pull request #240 from cwolferh/improve_check_for_all_nodes_joined

BZ #1101077 - Improve check for all nodes to join cluster