[Libvir] PATCH: Make test suite debug mode more friendly

[Jim Meyering]

"Daniel P. Berrange" <berrange at redhat.com> wrote:
> When the test suites fail, we have a DEBUG_TESTS=1 environment variable
> which can be set to show the full XML doc or string pair that failed to
> match. Unfortunately these docs can be quite large, so it is hard to
> spot the difference between the actual and expected output.
>
> So this patch introduces a virtTestDifference(actual, expect)  method
> which will trim the head & tail of the actual & expected strings until
> the point at which they differ. This gives immediate clear feedback on
> where the bug is
>
> Second, it will enumerate each test condition & pretty print align things
> a little better.

Looks good.