Fix authselect invocations to work with 1.0.2
    
    Since authselect 1.0.2, invoking an authselect command sequence
    like this:
    
    ['authselect', 'sssd', '', '--force']
    
    does not work: authselect barfs on the empty string arg and
    errors out. We must only pass a features arg if we actually have
    some text to go in it.
    
    This broke uninstallation.
    
    In all cases, features are now passed as separate arguments instead of one
    argument separated by space.
    
    Fixes: https://pagure.io/freeipa/issue/7776
    Signed-off-by: Adam Williamson <awilliam@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>