file plug-in testing.
The name and location of the xml results will be the same as for the
log file, but with the extension replaced by .xml.

Just some basic support is added which adds failed testcases when
a plug-in has a failure result, which should be the most common
case of failures.
Not all cases where we make errors in our test setup will generate
failed testcases yet, although they should show up in the number of
failures.
Disabled tests won't show up as skipped tests.
We also don't track time.