Azure: Allow to not provide tests to be ignored
    
    As for now, a list of tests which will be ignored by Pytest is
    mandatory. But actually, a list of tests to run is explicitly set
    in yaml config. And thus, 'ignore' list should be an optional field.
    
    This simplifies tests definitions to drop extra stuff.
    
    Fixes: https://pagure.io/freeipa/issue/8202
    
    Signed-off-by: Stanislav Levin <slev@altlinux.org>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>