repmgr: improve replication status checking during switchover

When checking the new standby's record in pg_stat_replication, keep
polling until the expected status is reported, and only give up
after a timeout was exceeded.

Previously repmgr would report an error if status was "startup",
even though this is not a problem.

repmgrd.c

@@ -1513,7 +1513,6 @@ do_master_failover(void)
 		 */
 		if (PQstatus(node_conn) != CONNECTION_OK)
 		{
-			/* XXX */
 			log_info(_("At this point, it could be some race conditions "
 					   "that are acceptable, assume the node is restarting "
 					   "and starting failover procedure\n"));