Break out Compute Manager unit tests

As we convert things to objects, it'll be easier to convert our compute
Manager tests to be true unit tests if they are in their own class.

There are currently a handful of tests that are true unit tests and
require no DB access.  These are now moved, subclassing from
test.NoDBTestCase.

Related to blueprint unified-object-model

Change-Id: I5e7ca3a94c32fff268e8b329f165198c873756e1
Merge "Break out Compute Manager unit tests"