tests/avocado/boot_xen.py: unify tags

Because all tests share the same tags, it's possible to have all of
them at the class level.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20231208190911.102879-10-crosa@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
1 file changed