Handle scheduling update live image create and install tests
This also rethinks the flavor naming strategy a bit: it seems
reasonable to just use the existing Workstation-live-iso and
Everything-boot-iso flavor names for these tests. This means
we have update test flavors that don't start with 'updates-',
so we have to rework some code that assumed they always would.
Signed-off-by: Adam Williamson <awilliam@redhat.com>