tests/qtest/migration-test.c: use 127.0.0.1 instead of 0

tests/qtest/migration-test.c: use 127.0.0.1 instead of 0

OpenBSD doesn't like :0 as an address, switch to using 127.0.0.1
in baddest; it's really testing the :0 port number that isn't allowed
on anything.

(The test doesn't currently run anyway because of the userfault
problem that Peter noticed, but this gets us closer to being able to
reenable it)

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20210719185217.122105-1-dgilbert@redhat.com>
Acked-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>