pylint: use yield_from for trivial cases
    
    Follow pylint recommendations (turned errors in recent pylint updates)
    and use PEP-380 syntax for subgenerators. This is supported by all
    Python 3 versions since ~2011.
    
    Signed-off-by: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Thomas Woerner <twoerner@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Rafael Guterres Jeffman <rjeffman@redhat.com>