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: I62b9029b984300194a00318de9a0111791bab07e
Closes-Bug: #1368661

tox.ini

@@ -13,7 +13,10 @@ setenv = VIRTUAL_ENV={envdir}
          ZAQAR_TEST_SLOW=1
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
-commands = python setup.py testr --slowest --testr-args='--concurrency 1 {posargs}'
+commands =
+    find . -type f -name "*.pyc" -delete
+    python setup.py testr --slowest --testr-args='--concurrency 1 {posargs}'
+whitelist_externals = find
 
 [testenv:pypy]
 setenv = {[testenv]setenv}