libvirt: remove pointless class in util test suite

The test_utils.py module had two separate test classes defined
for no real benefit. This is left over from merging tests from
two separate files together.

Change-Id: I808719955f90f7333aecbb9f3a1e19a377553edf
libvirt: convert test_vif.py to avoid DB usage

Remove use of the flavour APIs in the VIF test case avoiding
the need to hit the database. This allows conversion to the
NoDBTestCase which speeds up execution from 3 seconds to 0.3
seconds.

Partial-bug: #1369516
Change-Id: Ib0239b0f943baa1b1d81478b3b0d1e2ce1fb8722
Merge "libvirt: remove pointless class in util test suite"
Merge "libvirt: convert test_vif.py to avoid DB usage"