Use pop for checking messages with websocket
Use pop for checking messages with websocket

I1c94ad82c3b20cc331045c19d4a9987a701b081b fixed the issue in Zaqar where
the pop argument was wrongly named. We can now use it in the zaqar
collector to retrieve messages over websocket.

Change-Id: I0ce894b0eef7018a37db9ef9d1b43d8d20629bf0

openstack/os-collect-config