Add a tox test environment for random hashseed testing

The newer versions of tox by default enable a random PYTHONHASHSEED. However,
this breaks many Neutron unit tests, so PYTHONHASHSEED=0 is currently hard-
coded for Neutron's unit test environments.

We want to clean up the unit test cases that break with a random hashseed
(there are many). To be able to find the broken tests and then verify them,
we need to have an easy way of enabling random hashseed testing.

Partial-bug: #1348818

Change-Id: I51f05cdfa9f8728baabaf315b71e5defb26426b1

tox.ini

@@ -15,6 +15,12 @@ deps = -r{toxinidir}/requirements.txt
 commands =
   python -m neutron.openstack.common.lockutils python setup.py testr --slowest --testr-args='{posargs}'
 
+[testenv:hashtest]
+# This is the same as default environment, but with a random PYTHONHASHSEED.
+# You can also specify a specific hashseed (for test repeatability) as follows:
+#   tox --hashseed 1235130571 -e hashtest
+setenv = VIRTUAL_ENV={envdir}
+
 [testenv:functional]
 setenv = OS_TEST_PATH=./neutron/tests/functional
 commands =