fence_tool: new option to delay before join
    
    bz 460190
    
    Certain network/switch settings cause nodes to form partitioned clusters
    when they start up.  Add code to better cope with these initial partitions.
    The network partitions are a particular problem for two_node clusters where
    a node has quorum when it starts up on its own.
    
    This adds a new fence_tool option -m, e.g. fence_tool join -m <seconds>.
    It causes fence_tool to delay the join by up to <seconds> to allow all
    nodes in cluster.conf to become cluster members.
    
    This allows openais on the nodes to all see each other before starting
    the fence domain. So we join the domain *after* the nodes merge into a
    single cluster.  If we joined the domain *before* the cluster partition
    merged, then nodes end up being fenced unnecessarily.  (This is a similar
    idea to post_join_delay; a delay that gives us time to determine that a
    node in an unknown state is actually ok and doesn't require fencing.)
    
    Signed-off-by: David Teigland <teigland@redhat.com>