This change ensures that the structure of the unit test tree matches
that of the code tree to make it obvious where to find tests for a
given module. A check is added to the pep8 job to protect against
regressions.
The plugin test paths are relocated to neutron/tests/unit/plugins
but are otherwise ignored for now.
Change-Id: If307593259139171be21a71c58e3a34bf148cc7f
Partial-Bug: #1440834