Use queue's name and project to get messages

Mongodb's driver currently queries the queue's collection to get queue
id and then filter messages with it. Instead of storing the id, this
patches stores the queue name and the project in the message collection
and use that for querying messages.

It's safe to assume that the queue exists when messages are returned by
the query, however, posts operation will still verify queue's existence.

Fixes bug: #1207018

Change-Id: Iaa7bc3f1300b3349a5cfad5a9f6ecabb2f75e95e
Merge "Use queue's name and project to get messages"