Only schedule necessary tests for grouped critpath updates
    
    This builds on a bunch of enhancements to bodhi and greenwave
    I've been referring to as "grouped critical path". As of today,
    newly-created and edited updates aren't just "critical path" or
    "not critical path", but include info on which critical path
    groups they contain packages from. The greenwave policies have
    been updated to only require relevant tests for the groups the
    update is a part of. So we can refine scheduling to only schedule
    the necessary tests too.
    
    This is only done when flavors aren't explicitly specified. If
    the update is an older one that doesn't list the critpath groups
    but is just tagged as being critical path, we'll still schedule
    all flavors.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>