This patch did:
1. Add two commands: "set/get metadata" in API v2.
2. As v1.1 and v2 don't contain the queue.exist() function,
and the queue exist check has been done in server side. We
should only use it in v1.0.
3. As v1.1 doesn't support PATCH in zaqar server side,
we should not allow set metadata in v1.1.
DocImpact
Closes-bug: #1554326
Change-Id: I01b523ece09e87689516ecccf0c2c7795db46bb7
2854847fb4