They hadn't really been adapted to the new snapshot model.

This is just simpler than having to type it everywhere as a step
parameter.

So far this should be the only .feature that will run slower with the
new snapshot model, since we do not have the snapshot saved *after*
setting the Windows camouflage Tails Greeter option and logging in. We
could of course consider introducing a snapshot for that.

Crazy idea to consider: in the snapshot description structs, we could
introduce a "per-feature" flag that when true means that the snapshot
will be removed when the feature ends. That way we could have more
suitable "full background" snapshots.

This will make things much easier when converthing to the new snapshot
model.

When run in isolation, the read-only persistence scenario restored
from a snapshot where the default persistence source haven't been
created on the persistent media yet, which isn't what we want to test
here.