Remove .testrepository/times.dbm before test runs

"tox -e cover" may fail if run after "tox -e py27". This commit
tells tox to remove times.dbm between test runs.

Closes-bug: #1690751

Change-Id: Iea10b2bb5a72e8cf36afa5216b17aca3bc155ddc

tox.ini

@@ -11,7 +11,9 @@ deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 whitelist_externals = sh
                       find
+                      rm
 commands = find {toxinidir} -type f -name "*.py[c|o]" -delete
+           rm -f .testrepository/times.dbm
            ostestr '{posargs}'
 
 [testenv:fullstack]
@@ -38,6 +40,7 @@ commands = {posargs}
 
 [testenv:cover]
 commands =
+  rm -f .testrepository/times.dbm
   python setup.py test --coverage --testr-args='{posargs}' \
     --coverage-package-name=kuryr_kubernetes
   coverage report