Add tests for LinuxBridge and OVS agents

Fixes bug 988067

Patch introduces some more unit tests for LinuxBridge
and OVS agents.

Change-Id: I95b8856e75b303520af654b08854c6bd0bc5d7ea
Docstrings formatted according to pep257

Bug #1020184

quantum/agent/*
quantum/api/*

Change-Id: I206206b66b4adf5cda73a6bb709a0935d7efa821
Docstrings formatted according to pep257

Bug #1020184

quantum/common/*
quantum/db/*
quantum/debug/*
quantum/extensions/*

Change-Id: I8fdf72ae1702ef2a2652a1db683d8b31e09e6f84
Remove calls to policy.enforce from plugin and db logic

Blueprint make-authz-orthogonal

This patch implementes item #2 of the blueprint
Remove calls to policy.enforce when the policy check can be performed
safely at the API level, and modify policy.json to this aim.
This patch does not address enforce calls in the agent scheduler
extension, as that extension is currently not defined as a quantum.v2.api
resource class.
This patch also adds an API-level test case for the provider networks
extension, which was missing in Quantum and was necessary to validate
the API behaviour with the default policy settings.

Change-Id: I1c20a5870279bc5fce4470c90a210eae59675b0c
Merge "Add tests for LinuxBridge and OVS agents"
Merge "Remove calls to policy.enforce from plugin and db logic"
Merge "Docstrings formatted according to pep257"