When a MongoD process is part of a cluster, it can act (inclusively) as shard, config and now also as a router.

The actual process role is stored in the clusterRole global parameter, which can only assume the none, shard and config roles.

The goal of this ticket is to include the router role to the ClusterRole class and allow the non-exclusivity of roles. In this way the clusterRole global parameter can model MongoD processes configured to act as shard only, shard + router or router only.