Add "reset" action for Servers, ReplicaSets, and ShardedClusters

[llvtt]

Addresses #90.

The "reset" action does:

• Start any stopped machines in the replica set/cluster. This includes any servers/replica sets added since the replica set/cluster was created.
• Ensure that all members of the replica set are in one of states 1, 2, or 7.
• Ensure that all members respond to isMaster.

It does not:

• Clear any databases.
• Reset the oplog.
• Ensure the number of machines in the set/cluster are the same or have the same _ids as when it was originally started.

You can reset an entity by sending a POST request to /<entity>/<id> with a body of {"action": "reset"}.

[gjmurakami-10gen]

LGTM!