Pass missing parameter to dbusmock bluez PairDevice function

Required as per python-dbusmock 0.27.5

See also:

• https://github.com/martinpitt/python-dbusmock/commit/fae4be7f49c0861ff903f350d5c3f91d08cae8ad
• https://github.com/martinpitt/python-dbusmock/commit/8968284e8bdc2347ade258b5f7864a5698455532