-Switch functional job to run under python3
-Create a functional job to run under python2
-Create a tempest job to run under python2
-Create tox env to run functional tests under python3
-Validate if `USE_PYTHON3` is set to `True` to call
the correct env for tests
-Remove hardcoded path for client when running functional tests
- Update tests failures to work for python2 and python3
Change-Id: I55abc999f6f397b171d05fd9e9b39d833ca95e55
9b881cb973