Remove dsvm-cells tests from places they don't do anything

The dsvm-cells tests only run exercises, and basically only test that
1 guest boots with a volume. They aren't relevant to horizon, heat, or
keystone as there isn't sufficiently high probability that changes
there can impact the success of this test.

Change-Id: I9b9d65f3bb02283542bcde0d95f6e79eeb0bd23d
Merge "Remove dsvm-cells tests from places they don't do anything"