Ensure to install latest neutron from master
Ensure to install latest neutron from master

neutron-vpnaas-dsvm-functional-sswan job requires neutron master branch
but after neutron was added to g-r neutron queens is installed.
Ideally this can be handled by tox-siblings with zuulv3 native job,
but it requires several efforts. This commit tries a work-around
just to pass the current broken func test.

Change-Id: I91fa5222031ad129f7fdfba5bf1bcb09c6d196ac

openstack/neutron-vpnaas,openstack/neutron-vpnaas