feat(api): GET and HEAD methods on queue

To allow

    GET/HEAD /queues/a-queue

gives users an intuitive approach to test whether the queue exits,
while the URI above is returned as the Location header by a queue's
PUT method.

Implements: blueprint queue-get-and-head
Fixes: bug #1207075

Change-Id: Iefd3236a739b1a5d959efb489fc2b966ee893599
Merge "feat(api): GET and HEAD methods on queue"