Add `use-sharding` option and stuff

Concerning #167.

The first patch is to add `use-sharding` option for MongoDB. Sharding itself hasn't been added yet.

The other is to separate a common part of `MongoDBStandaloneLauncher` into `MongoDBLauncher`, as it can be used in another MongoDB instance launchers.

@sgkim126 @murmur76 @kimchoco, please review this.