Robust Environment Variables

[ric-evans]

continuing from #70:

mqclient is used pretty low in the stack in skydriver and the skymap scanner, and it has a lot of configurable parts: timeouts (4ish), auth token(?), and prefetch. These are mostly init args from Queue, but the arg-forwarding can be error-prone and requires knowledge of multiple package call levels. So, let's replace these optional args' default values with env vars.

[ric-evans]

It's not a usual use case to have only one queue per shell. This type of config better fits one layer up, at the application level. See Observation-Management-Service/ewms-pilot#11