Upgrade tox to 1.6

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.

Change-Id: Ib011a9add595696f5db5fe596db9d3d60f46d038
Fixes-Bug: #1233213
Replace Cheetah with Jinja2

Other projects are already using Jinja2.

Partial port of nova commit fa0d61084e50c264f3231f997e4243b8037919f8

Change-Id: Id87c8dff3c60ef7155c1cd940ada8316678711d6
Closes-Bug: Bug #1233251
Merge "Replace Cheetah with Jinja2"
Merge "Upgrade tox to 1.6"