Enforce log hints in neutron.plugins.plumgrid

This change enforces log hints use and removes debug level log
translation, modifications are validated through a hacking rule and
the change respects loggging guidelines.

Validate that hacking rules apply to directories:
    - neutron/plugins/plumgrid

Change-Id: Ie85abb93cdbe50bdd56c9f987784baf4c4dd631d
Partial-bug: #1320867
Merge "Enforce log hints in neutron.plugins.plumgrid"