Poll glance directly

Changes the Qonos snapshot worker to poll for image status, get image lists, and delete images directly via the Glance API rather than going thru Nova.
How about using 'get' operation on response dict instead of direct member access? Direct member access results in an ugly KeyError if for some reason we don't the expected response. Talking about unexpected responses, how about we check that the response dict actually contains the 'access' and 'token' element before accessing them?