libvirt: convert HostStateTestCase to avoid DB usage

The HostStateTestCase test case does not do anything DB
related. Convert it to NoDBTestCase to avoid DB setup penalty.
This improves perf from 1.7s to 0.2s

Partial-bug: #1369516
Change-Id: I0b1030b8a4e8c32f24c5b3a08ff86fa5bad06937
Merge "libvirt: convert HostStateTestCase to avoid DB usage"