test_xmlrpc: Use absolute imports
In Python 3, a module from the current package can be imported
either with the absolute name or by using an explicit relative import.
Part of the work for https://fedorahosted.org/freeipa/ticket/4985
Reviewed-By: Martin Basti <mbasti@redhat.com>
Reviewed-By: Petr Spacek <pspacek@redhat.com>