Discussion: remove dependency on neutron.manager in policy

This is a discussion bug in regards to the neutron-lib effort.
We want to break dependencies with neutron.manager and are specifically looking at uses of get_instance().

Today policy uses NeutronManager.get_instance() to get reference to a plugin [1].

Is there a way we can refactor [1] to not use get_instance()?

Given some direction from the gluon team, I'm happy to do the refactoring. Or someone from the team and drive it.

[1] http://git.openstack.org/cgit/openstack/gluon/tree/gluon/policy.py#n260