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.

Closes-Bug: #1368661

Change-Id: Idf3a46d8c95806f2d2ce28ce84ced12b625e53df

tox.ini

@@ -13,6 +13,7 @@ setenv = VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 commands =
+  find . -type f -name "*.pyc" -delete
   python -m nova.openstack.common.lockutils python setup.py test --slowest --testr-args='{posargs}'
 
 [tox:jenkins]