rgw_rest_user: Create RESTful interface for administrative user operations.

Allow for user creation, modification, and removal through the
Admin API. Also exposes a user's access keys, subuers, and admin
capabilities as subresources to the RESTful /{admin}/user endpoint.

Signed-off-by: caleb miles <caleb.miles@inktank.com>
rgw_rest_bucket: Create RESTful interface for admin bucket operations.

Allow for bucket removal, linking, un-linking, policy retrieval, object
removal, and index repair through the Admin API. Also exposes a bucket's
index, objects, and policy as subresources to the RESTful /{admin}/bucket
endpoint.

Signed-off-by: caleb miles <caleb.miles@inktank.com>