Add '*.pyc' clean up for unit_tests

After updating code from actual branch we still use old *.pyc files.
It can give an unexpected result, for instance, a lot of tests are
broken due to unknown reasons.
This patch fixes this issue.

Change-Id: I3bdbad9748dc3d94d6d8914156604eab7ad877a0

tox.ini

@@ -12,6 +12,7 @@ setenv =
   NOSE_OPENSTACK_SHOW_ELAPSED=1
 whitelist_externals =
   bash
+  find
 deps =
   -r{toxinidir}/requirements.txt
   -r{toxinidir}/test-requirements.txt
@@ -49,7 +50,9 @@ commands =
   {[unit_tests]commands}
 
 [unit_tests]
-commands = bash {toxinidir}/tools/unit_tests.sh {envpython} {toxinidir} {posargs}
+commands =
+    find . -type f -name "*.pyc" -delete
+    bash {toxinidir}/tools/unit_tests.sh {envpython} {toxinidir} {posargs}
 
 [testenv:pep8]
 usedevelop = True