Authentication & replset changes

* Made user & passwd variables global so they can be referenced again. Added both to all connects that were missing them.
* Added check for authentication results and exit if failed.
* Added check for replica set command line option
(If you set replset in the connect string pymongo will always connect to the master)
* improved host_node check to use host given on cmd-line
(host_status["me"] was always the primary. Reason for this was the replset option being set. This is not really needed after the fix above, but it is still better than the old check imho)