Bug 3999: Create internal service to access restconf

Bug 3999: Create internal service to access restconf

There are use cases for invoking restconf from internal code. However
issuing an HTTP request is problematic as one would need to know the
credentials and scheme (http or https).

So I added a JSONRestconfService interface and implementation with CRUD
methods that call the JSON readers/writers and RestconfImpl internally.
The implementation is advertised as an OSGi service via the config
system for consumption by clients.

I only added a service for JSON - an XML service could be added as well
later.

Change-Id: I5d1304c568c9be9c204afea68aadc0306bac50b3
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>