Support testing the semi-official live-respins, more fedfind
    
    Summary:
    The point of this change is to support testing the 'respin'
    composes that are built by volunteers and live in live-respins
    in the alt tree on the mirrors. These are considered to be
    'semi-official', and the maintainers asked if we could test
    them. This depends on the latest fedfind git master ATM (I'll
    cut a release soon).
    
    To make this possible we kinda have to go back to using fedfind
    more. I was hoping when I initially dumped the use of fedfind
    that fedfind might actually go away soon, but for a bunch of
    awful reasons that make me want to drink, this seems very
    unlikely. These live-respins composes aren't built with Pungi 4
    and don't have metadata, so we kinda have to go through fedfind
    to understand them.
    
    I think the changes to use fedfind actually make the scheduler
    code a bit nicer, though. Especially it lets us use a less
    stupidly-nested 'WANTED' structure (now a list not a dict).
    
    I have tried this out on staging (that's why there were a bunch
    of needle commits to the tests), and it works. The stupid fedmsg
    consumer hack is untested as yet (but should be tested quite
    soon). I'm not married to that, if you hate it we can just drop
    it and set up a cron job or something instead.
    
    Test Plan:
    Try testing the current live-respins compose, see
    if it works. Check I didn't break anything else.
    
    Reviewers: jskladan, garretraziel
    
    Reviewed By: garretraziel
    
    Subscribers: tflink
    
    Differential Revision: https://phab.qadevel.cloud.fedoraproject.org/D1067