Fix modules Restconf call for mounted devices

Restconf was relying on the remote devices to contain restconf yang model. Now
Restconf relies on the controller's schema context when it serializes the
modules response.

Change-Id: Ib406d0082a5aafb7e894440ee5f75e5032ea35ba
Signed-off-by: Maros Marsalek <mmarsale@cisco.com>