add encrypted workstation upgrade tests (current and previous)
    
    Summary:
    This requires us to handle decryption each time we reboot in
    the upgrade process, so factor that little block out into the
    base class so we don't have to keep pasting it. It's also a
    bit tricky to integrate into the 'catch a boot loop' code we
    have to deal with #1349721, but I think this should work. There
    is a matching openqa_fedora_tools diff to generate the disk
    image.
    
    Test Plan:
    Run the tests, check that they work, run the other
    upgrade and encrypted install tests and check they still work
    properly too.
    
    Reviewers: garretraziel
    
    Reviewed By: garretraziel
    
    Subscribers: tflink
    
    Differential Revision: https://phab.qadevel.cloud.fedoraproject.org/D922