Fix route for bulk-get message by ID

This patch includes the following changes:

* /v1/queues/my-queue?ids=1,2,3 => /v1/queues/my-queue/messages?id=1,2,3
* Update Location header to suite
* Always return the same schema for location header, regardless of the
  number of messages POSTed.

Change-Id: I4559222e8f4685af1020c2743c26de699aef30dd
Fixes: bug #1194571
Fixes: bug #1165102
Merge "Fix route for bulk-get message by ID"