Use upper constraints for all jobs in tox.ini
Use upper constraints for all jobs in tox.ini

Openstack infra now supports upper constraints for
all jobs. Updated tox.ini to use upper constraints
for all jobs.

Change-Id: I94f57e294a7de91d45c26b1f90caad67b0974718
Closes-Bug: #1614361

openstack/python-neutronclient,noironetworks/python-neutronclient,huntxu/python-neutronclient,Juniper/python-neutronclient,Juniper/python-neutronclient,huntxu/python-neutronclient,openstack/python-neutronclient,noironetworks/python-neutronclient