mongo: check all addresses when deciding if machine is master

The recent fix for LP #1397376 meant that on MAAS the replicaset master address no longer matches the address returned by SelectPeerAddress - no state server thought it was the master. This breaks upgrades among other things.

All machine addresses are no compared against the replicaset master address.

Fixes LP #1403200.

(Review request: http://reviews.vapour.ws/r/648/)