The `ZTest` GTest fixture is used for both VM and not VM tests, however the implementation requires VM. The not VM tests which use it are only interested in a sub-set of its features.

I propose we split `ZTest` into a hierarchy of fixtures, one for not VM tests, and the other for VM tests.

I could not find an easy way to identity which category of test a fixture is used in, so for now we just have to be diligent to use the appropriate fixture.