tests/functional: Convert the hotplug_blk avocado test

By using the serial console instead of ssh for executing commands
in the guest, we can convert this test to the functional framework.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20250130192712.19542-1-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
4 files changed