Have tox install via setup.py develop
Have tox install via setup.py develop

tox 1.6 was released, which means that we can now take advantage of the
feature we added to it - which is using setup.py develop to install the
code into the virtualenv. The logic was taken from run_tests.sh - so the
performance issues around using tox vs. using install_venv should now be
gone.

run_tests.sh is still needed to handle the ui switching between
parallel, single and debug modes to testr.

Change-Id: Ida5e440d1bdb9f8e9031277ea53a02d2ef171438

n0ano/gantt,n0ano/gantt