tests/functional: Convert the migration avocado test

tests/functional: Convert the migration avocado test

Now that we've got a find_free_port() function in the functional
test framework, we can convert the migration test, too.
While the original avocado test was only meant to run on aarch64,
ppc64 and x86, we can turn this into a more generic test by now
and run it on all architectures that have a machine which ships
with a working firmware. To avoid overlapping with the migration
qtest, we now also test migration on machines that are not covered
by the migration qtest yet.

Acked-by: Fabiano Rosas <farosas@suse.de>
Message-ID: <20250103074308.463860-1-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>