totemconfig: Make sure join timeout is less than consensus

The thesis contains this paragraph:

  "The Join timeout is shorter than the Consensus timeout and is used
   to increase the probability that Join messages from all currently
   working processors are received during a single round of
   consensus."

Empirically I can confirm that making join less than consensus can
cause havoc with a cluster so I think we should enforce this.

Signed-off-by: Christine Caulfield <ccaulfie@redhat.com>
Reviewed-by: Jan Friesse <jfriesse@redhat.com>