Removal of fake-capabilities test from qemuxml2argvtest

[Peter Krempa]

Hi,

recently I've got very annoyed that we still have a very large amount of
tests in qemuxml2argvtest which use DO_TEST or some other fake-caps
test.

While I can see value of fake-caps test for negative cases (but I'd
prefer actually real-caps with capability masking) I don't think there's
much value in keeping the DO_TEST fake-caps stuff around.

Namely in most cases it doesn't test anything useful which could be
encountered in real world.

I propose that we convert all DO_TEST cases to:

- DO_TEST_CAPS_LATEST
- and possibly a amount of version-bound tests based on:
    - oldest supported version?
    - versions in popular distros?
    - none?
    - any ideas?

For the negative cases we can think of the caps masking or other
approach but getting rid of DO_TEST would IMO be a great step forward in
terms of usefullnes of our unit tests.

Any feedback is welcome

Peter