This patch updates the config for tox/zuul by:
- Switching the test running over to stestr like all other projects.
- Adding local tox targets for pep8, py27 and py3; see .
- Removes the git install of neutron and sfc from the testenv tox
target as those should be applied generically by the testenv target;
zuul will handle them in the gate and testenv:dev locally.
- Zuul.yaml is updated to properly define neutron and
sfc as required projects so they are pulled into the gate.
- Lower constraints job, tox target and constraints added.