Set the python hash seed that tox uses to 0

The current trove unit tests don't work correctly with the random
hash seed that the new tox sets by default.

This change forces the new tox to use 0 as the hash seed which
should unblock the gate until we can fix the trove unit tests
to run correctly with a random hash seed.

This change will probably need to be backported to the stable
branches to ensure that the tox tests keep working there as well.

Change-Id: Ib5c6d4d166c847ce94ec70740c5753d338687865

tox.ini

@@ -4,13 +4,16 @@ minversion = 1.6
 skipsdist = True
 
 [testenv]
+# Note the hash seed is set to 0 until trove unit tests can run with
+# a random hash seed successfully.
 setenv = VIRTUAL_ENV={envdir}
+         PYTHONHASHSEED=0
 usedevelop = True
 install_command = pip install -U {opts} {packages}
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 commands = {envpython} run_tests.py
-	    python setup.py testr --slowest
+           python setup.py testr --slowest
 whitelist_externals = bash
 
 [tox:jenkins]
@@ -62,4 +65,3 @@ commands = openstack-doc-test --check-build {posargs}
 
 [testenv:publishdocs]
 commands = openstack-doc-test --check-build --publish --force
-