Return 400 for invalid Json for api v2

For invalid json, a ValueError is returned by python's json decoder.
On v2, we now catch this and return a 400 (invalid_json)

Change-Id: Idb76f051c6d09d5fd26f0a44fa75a0ffd9f37b6a
Closes-Bug: #1288456
Merge "Return 400 for invalid Json for api v2"