Fix claims on non-existing queue on swift
Fix claims on non-existing queue on swift

This returns an empty list instead of an error if we try to claim
messages on a queue that doesn't exist yet.

Change-Id: Ia92774ef1c55a371e37fc845511a5dceb8f92c00
Depends-On: I7e2128f3a5608ed9a41d1e18bd72d771a2a4ddb3
Closes-Bug: #1754061

openstack/zaqar,openstack/zaqar,openstack/zaqar,openstack/zaqar