Update the HTTP 500 JSON structure to match oslo

Update the JSONRenderer to ouput fault JSON in the structure expected by
clients based on the oslo common code. This change also adds test
coverage for the renderer.

Change-Id: I36f495cac687c3833a765ad91f9d834964fb27bd
Closes-Bug: #1276465
Merge "Update the HTTP 500 JSON structure to match oslo"