Make python33 gate voting for solum project

As we can see that the latest merge [1] to the master is passing
python33 gate. Let us enable it.

[1] https://review.openstack.org/#/c/57719/

Change-Id: I3f14b44d28bfaa9f7a6beb1567e7063d5f400077
Merge "Make python33 gate voting for solum project"