SERVER-14616 replace BSONObj with ReplSetHeartbeatArgs in processHeartbeat
SERVER-14318 replace check() in replset_commands with ReplCoordinator::checkReplEnabledForCommand
SERVER-14673 eliminate unnecessary isShutDownOkay() method from ReplicationCoordinators
SERVER-14616 replace BSONObjBuilder with ReplSetHeartbeatResponse in processHeartbeat
SERVER-14616 add setters and toBSON to ReplSetHeartbeatArgs