This patch retires the NSX MH plugin by:
- Deleting the nsx_mh plugin and unit test code.
- Using the NSX-V and V3 plugin test base classes where needed.
- Removing any extensions that are MH specific.
As part of the python 3 first effort , this patch adds UT support for
python 3.6 by:
- Updating the zuul.yaml to include the py36 template and jobs.
- Adding a py36-dev target to tox.ini for local testing.
- Updating the upper constraints to use master rather than stable/rocky.
- Updating the version of eventlet used as previous 2x.x versions had
a python 3 bug for monkey patching.
- Consolidating the eventlet monkey patching in the code.
There is no reason to do it for the plugin since it does not split
namespace into pieces. By doing it, we avoid the need to generate and
ship .pth file with the package.