Remove *.pyc files before running tox tests

Modified tox.ini to remove any .pyc file before running tests.
Also, now it removes all the __pycache__ folders which was also
in the bug report.

Change-Id: I2f60751b155f8098b746339c12406b934bcdbcf9
Closes-Bug: #1525852

tox.ini

@@ -5,12 +5,16 @@ skipsdist = True
 
 [testenv]
 usedevelop = True
+whitelist_externals = find
 install_command = pip install -U {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
-commands = python setup.py testr --slowest --testr-args='{posargs}'
+commands =
+  find . -type f -name "*.pyc" -delete
+  find . -type d -name "__pycache__" -delete
+  python setup.py testr --slowest --testr-args='{posargs}'
 
 [testenv:pep8]
 commands = flake8