Avoid use of replicaSet argument in pymongo.Connection() call

On RedHat 5 EPL package for pymongo module (version 1.9) does not support
pymongo.Connection() call with replicaSet argument. Doing the replicaset name
check manually after the connection acquired is functionally equivalent for
check_replica_primary()
Merge pull request #69 from jeremybaumont/master

Avoid use of replicaSet argument in pymongo.Connection() call