Improves pgxc_ctl behavior to

1) When issuing pg_ctl start.   Added -w option for better synchronization.

2) At pinging coordinator/datanode, when ping does not detect the node,
   retries three times with 100 millisecond interval just in case.

Conflicts:

	contrib/pgxc_ctl/coord_cmd.c

As well as incorrect nodePing() result evaluation when initializing
coordinator slave.