Currently if set_snapshot_number is true, it uses "Snapshot" as prefix.
In some cases it's necessary to use a different one. This can now be configured
using the "snapshot_number_prefix" option.
It takes a long time to sync the repos but ISOs are very quick. This lead
to the problem that openQA already started syncing the build while the
repo was synced up. As the repository is set to unpublished in between
the calls, openQA has no chance to see that more is to come.
So if we release the slow products first, openqa has a better chance to
catch up.
Currently everything needs to have a maxsize defined, but for most it doesn't
make sense. So only keep those which do and don't impose a limit by default.
totest_images_repo defaults to product_repo if unset.
That's not exactly the same behaviour as before (following the releasetarget),
but should cover all current projects.
