Ticket 47622 - Automember betxnpreoperation - transaction not aborted when group entry does not exist
    
    Bug Description:  If the group defined in the automember plugin does not exist, than any add operation
                      that should trigger an update, succeeds even though the automember update failed.
    
    Fix Description:  Return an error if a automember post operation update fails - previously we always
                      returned success.
    
                      Updated plugin_call_func() to check the result of betxn postop plugins.
    
                      Also added return text to the result message when a betxn plugin fails.  This is
                      useful for clients to explain why the operation failed.
    
    https://fedorahosted.org/389/ticket/47622
    
    Jenkins: passed
    Valgrind: passed
    Coverity: passed
    
    Reviewed by: rmeggins(Thanks!)