Remove .testrepository/times.dbm from tox.ini

1. What is the problem
When running tox for the first time, if you run "tox -e py35" ahead of
"tox -e py27", then "tox -e py27"  will fail. And if you run "tox -e
py27" ahead of py35 test, the py35 execution fails with an error saying
"db type could not be determined". In other case, If you execute "tox
run" instead of running py27, py35, pep8 and pypy test respectively, the
py35, pypy and pep8 can all pass the test except the py27. This bug is
reported here[1].

2. What is the solution to the problem
This issue can be solved by removing .testrepository/times.dbm
from tox.ini.

3. What the features need to be implemented to the Tricircle
to realize the solution
None.

[1] https://bugs.launchpad.net/testrepository/+bug/1229445

Change-Id: I497aa835fc5551b7422741216aa1c702f7aa6f0b

tox.ini

@@ -14,7 +14,9 @@ setenv =
 deps =
     -r{toxinidir}/test-requirements.txt
     -egit+https://git.openstack.org/openstack/neutron@master#egg=neutron
-commands = python setup.py testr --slowest --testr-args='{posargs}'
+commands =
+    rm -Rf .testrepository/times.dbm
+    python setup.py testr --slowest --testr-args='{posargs}'
 whitelist_externals = rm
 
 [testenv:releasenotes]