This is just a cleanup work to hide some of the private state of
ReplSetTest so it is easier to encapsulate and add new logic. Also enables
strict mode.
Changes the existing architecture of having a mongobridge process for
each unidirection link between two mongod processes in a replica set to
having a single mongobridge process per node in the replica set. The
mongobridge process is able to distinguish between connections from
different hosts by using the "hostInfo" field in the initial isMaster
command request.
