tests/avocado/boot_xen.py: use class attribute

Rather than defining a single use variable, let's just use the class
attribute directly.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20231208190911.102879-11-crosa@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
1 file changed