replica set duplicate node fix

The replicaset recipe was attempting to configure mongo with duplicate nodes. This is because the library was failing to successfully check that the node was already in its list of members. This fix overcomes this by not comparing node objects with members but only comparing the fqdn of the node object with members. 

Also adding forwards compatibility support for installing "mongo" gem via chef_gem. 

Also changed the way that Mongo::ReplSetConnection.new is called from the mongodb library. The arguments didn't match those needed for the mongo gem (v 1.8.3)