Tests: remove .testrepository/times.dbm in tox.ini
Tests: remove .testrepository/times.dbm in tox.ini

Existance of this file causes py3* tests to fail if
run after py27. This patch adds cleaning up of this
file before running py3* tests.

Closes-Bug: #1229445

Change-Id: I9e908f2520c39c2f97fc5a841d604a0cf4406621

kevin-zhaoshuai/zun,kevin-zhaoshuai/zun,kevin-zhaoshuai/zun