cman: fix quorum recalculation when a node is externally killed
    
    This patch fixes a condition where quorum would be incorrectly recalculated
    if a node was removed from the cluster using the cman_kill_node call.
    This call is used by qdisk and can cause a cluster to continue operating
    when too few nodes are left in the cluster for a legitimate quorum.
    
    rhbz#596046
    
    Signed-off-by: Christine Caulfield <ccaulfie@redhat.com>