tests/avocado/boot_xen.py: merge base classes

While it's a good practice to have reusable base classes, in this
specific case there's no other user of the BootXenBase class.

By unifying the class used in this test, we can improve readability
and have the opportunity to add some future improvements in a clearer
fashion.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
Message-ID: <20231208190911.102879-9-crosa@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
1 file changed