Don't enable oslo-incubator py33 for stable/havana

Py33 gate was enabled for oslo-incubator as part of Ia38b9ad2d6b2180459653017b308841eb78bda89

This change, however, enabled the gate also for stable branches, which
was not the goal of the patch. This patch intends exclude this job for
stable/grizzly and stable/havana.

Change-Id: I15cfc2d7d567a3c45dff803ebac8eb372ff09379
Merge "Don't enable oslo-incubator py33 for stable/havana"