Have non-English tests do graphical install and login
    
    Summary:
    The non-English tests so far did not test that graphical login
    worked as expected, which is a fairly large hole. With this
    change, they should do a Workstation install and test login to
    both GNOME and the console works as expected. KDE is not yet
    tested.
    
    As part of this we tweak the implementation of keyboard layout
    switching in graphical environments to use a generic function
    in main_common which can handle both anaconda and desktops
    (just GNOME at present, but should extend easily to any desktop
    with a known switcher key and a visible layout indicator),
    replacing the anacondatest class method. I kinda don't like that
    the test has to specifically tell the function when it's in
    anaconda, but I don't think I want to start experimenting with
    a global 'test phase' openQA variable or anything like that at
    present.
    
    Fixes T842.
    
    Test Plan:
    Run the French and Russian install tests and check
    they work as expected. Also run an English Workstation install
    if you like, and make sure that didn't break. This change is
    live on staging ATM, seems to work fine.
    
    Reviewers: jskladan, garretraziel
    
    Reviewed By: garretraziel
    
    Subscribers: tflink
    
    Maniphest Tasks: T842
    
    Differential Revision: https://phab.qadevel.cloud.fedoraproject.org/D1071