tests: testQemuCapsIterate: Pass prefix and version to callback

tests: testQemuCapsIterate: Pass prefix and version to callback

Right now we're passing a "base" string that contains both,
separated by an underscore. Some changes that we're going to
introduce later will require us to have the version number on its
own, and instead of delegating the task of splitting the two apart
to the callback it make more sense to perform it upfront.

This change results in quite a bit of churn because we're now
using the version number only, without the prefix, to calculate
the dummy microcodeVersion.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Jiri Denemark <jdenemar@redhat.com>