Skip negative compute quota tests that don't work with Neutron

Change I5187a109f0bacb1f3afa4276b3d73f47fd53ad87 re-enabled some
negative quota tests for compute but they don't work if you're using
Neutron due to nova bug 1186354.

There is a patch up for the bug here:

https://review.openstack.org/#/c/43822/

but it's taking awhile to land so we should skip the tests until that's
working.

Partial-Bug: #1186354

Change-Id: I0458f8cf95585962638a82da34397071e34a1940
Merge "Skip negative compute quota tests that don't work with Neutron"