Delete python bytecode before every test run

Bring over the cleaning line from run_tests.sh for the pyc files to
all the tox runs.

This should eliminate the need to clean -x -i to kill pyc files in
your local directory to get tests to pass.

Change-Id: I4e06e17e97c5416e1f9283d5f0a4f5d6338e1ce7
Closes-Bug: #1368661

tox.ini

@@ -9,7 +9,10 @@ usedevelop = True
 install_command = pip install -U {opts} {packages}
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
-commands = python setup.py testr --slowest --testr-args='{posargs}'
+whitelist_externals = find
+commands =
+  find . -type f -name "*.pyc" -delete
+  python setup.py testr --slowest --testr-args='{posargs}'
 
 [testenv:pep8]
 commands = flake8