The model_query module is in neutron-lib and the CommonDBMixin will
eventually be removed. This patch swiches use of the _model_query
method over to query_with_hooks from neutron-lib.
This patch also bumps the neutron-lib version up to 1.20.0
Change-Id: Ie8e9123cb2c58b4bde717648f2cfff7664da434e