Add delete *.pyc command before executing ostestr

This commit adds a command for deleting *.pyc before executing ostestr
with tox. This patch would help that removing unnecessary *.pyc files
when we rename, move or remove *.py ones.

Change-Id: Ifa0eb18a10c7e7ee7e15ce7cc69a1b007a016a76

tox.ini

@@ -8,9 +8,12 @@ usedevelop = True
 install_command = pip install -U {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
+whitelist_externals = find
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
-commands = ostestr {posargs}
+commands =
+         find . -type f -name "*.pyc" -delete
+         ostestr {posargs}
 
 [testenv:pep8]
 commands = flake8