Initial pecan structure

Initial pecan structure

This patch is the initial work for the pecan refactor.

* Adds pecan as a requirement
* Adds a simple API server named 'neutron-dev-server' for use
  when neutron server is not deployed in a web server
* Wraps the app with the openstack request ID middleware
* Adds a basic V2 controller that breaks out requests by method
* Adds functional tests to ensure request ID is set and requests
  are properly sent to the V2 controller.

Partially-Implements: blueprint wsgi-pecan-switch
Co-Authored-By: Brandon Logan <brandon.logan@rackspace.com>
Co-Authored-By: Mark McClain <mark@mcclain.xyz>
Change-Id: Ic9697ff30ab8359b62ce01eb73dc927065a8e3e6