umt testflinger: Support querying queues via testflinger API
The queues.json doesn't seem to be alive at the moment so add support for
querying the testflinger API directly to get the list of available queues
as well as their associated images.
umt: emit warnings in umt download step as well as umt check
umt emits some specialized warnings on a per package basis but only
during `umt check`. This is late in the update preparation process,
and often a preparer has already tripped over some of these issues
before they even get to the point of running `umt check`.
To address this, split out the warning generation into a separate
function so that they also can be emitted during `umt download`,
whensomeone is at the beginning of preparing an update, and will
hopefully take them into account when doing the preparation.
Also included are an added commit for mongodb, an additional warning
for curl, and reformatting the data structure.
