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: I415b7c9ed1c244fb08fc1ce9581e040656c65f09
Closes-Bug: #1368661

tox.ini

@@ -9,7 +9,10 @@ install_command = pip install -U {opts} {packages}
 setenv = VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/test-requirements.txt
        -r{toxinidir}/requirements.txt
-commands = /bin/bash run_tests.sh -N {posargs}
+whitelist_externals = find
+commands =
+ find . -type f -name "*.pyc" -delete
+ /bin/bash run_tests.sh -N {posargs}
 
 [testenv:pep8]
 commands = /bin/bash run_tests.sh -N --pep8