vpnaas: Turn on python3 jobs
vpnaas: Turn on python3 jobs

The dependent commit enables this for neutron-vpnaas, but only
for master and not juno or kilo.

Change-Id: I5007b93dd8cca76c240eccad217b6d7df1ddeafd
Depends-On: Ibde058c11804a783b4477ecf4d59c1af99bd73fc
Signed-off-by: Kyle Mestery <9cfbda34e625c7b0454bcb19a48d07c46f9097d2@mestery.com>

noorul/os-project-config,noorul/os-project-config,Tesora/tesora-project-config,dongwenjuan/project-config,coolsvap/project-config,openstack-infra/project-config,Tesora/tesora-project-config,coolsvap/project-config,openstack-infra/project-config,dongwenjuan/project-config