Add tempest-devstack-vm-neutron-large-ops job

Add neutron variant of the -tempest-devstack-vm-large-ops job.

The large-ops job checks for performance/scale issues in OpenStack. So
far we have only been running for nova-network, but we should be running
it for neutron too.

This patch introduces the job as non-gating, to make sure people get
familiar with the test and to make sure it is stable. Once its working
we can move it to gating.

Change-Id: Ie8d2e66812abae0ba6c18f78c9ff7c1afaab4609
Merge "Add tempest-devstack-vm-neutron-large-ops job"