py3: Add py34 test environment to tox
py3: Add py34 test environment to tox

Add a py34 test environment to tox.ini using a whitelist
of tests which pass on Python 3. Currently, only test_exceptions.py
of test/unit/common/ is run on Python 3

Change-Id: I5c8a9fe7b9635f1acab8f401908975fc6fc58c7a

matthewoliver/swift,psachin/swift,redbo/swift,thiagodasilva/swift,openstack/swift,nadeemsyed/swift,matthewoliver/swift,notmyname/swift,larsbutler/swift,williamthegrey/swift,smerritt/swift,tipabu/swift,hurricanerix/swift,thiagodasilva/swift,revoer/keystone-8.0.0,matthewoliver/swift,openstack/swift,aerwin3/swift,swiftstack/swift,openstack/swift,prashanthpai/swift,revoer/keystone-8.0.0,daasbank/swift,aerwin3/swift,clayg/swift,redbo/swift,hurricanerix/swift,openstack/swift,matthewoliver/swift,nadeemsyed/swift,levythu/swift,psachin/swift,tipabu/swift,smerritt/swift,psachin/swift,smerritt/swift,prashanthpai/swift,clayg/swift,tipabu/swift,larsbutler/swift,williamthegrey/swift,hurricanerix/swift,nadeemsyed/swift,clayg/swift,rackerlabs/swift,notmyname/swift,clayg/swift,levythu/swift,daasbank/swift,nadeemsyed/swift,notmyname/swift,hurricanerix/swift,tipabu/swift,swiftstack/swift,smerritt/swift,notmyname/swift,swiftstack/swift,psachin/swift,rackerlabs/swift