Add helpers to be able to "synchronize" nodes in the cluster

When non-founder nodes call:
  PacemakerHelper.wait_for_mark_from_founder(node, cookbook_name, "pki-sync", node[:keystone]["crowbar-revision"])

they will be blocked until the founder calls:
  PacemakerHelper.set_mark_if_founder(node, cookbook_name, "pki-sync", node[:keystone]["crowbar-revision"])