corosync: Ensure that we always use authkey from founder when in Crowbar

When the corosync cookbook is running orchestrated by Crowbar, then we
know that there will be a member of the cluster that is the pacemaker
founder, and we will always use the authkey from that node.

When not running orchestrated by Crowbar, then we will just use the
first authkey we find.
Fix founder attribute to be a boolean, not a string
Ensure that pacemaker-cluster-member nodes are not marked as founders

Just as a safety net to protect against users doing weird things, we
override the pacemaker.founder attribute to false for non-founders.
Remove tests to skip writing authkey file

This really shouldn't be needed: chef will not write the files if they
already have the right content, and if they don't, we want chef to write
the files.