We don't really have the "infrastructure" set up yet to have proper log
output at that point, but we can always just show the log output as part
of the exception.
We now divide all timeouts by ten for xfailing tests, with the hope to
still catch newly passing tests, but not spend too much time waiting.
With a quick test, this reduced the testsuite run length from 12 to
7-8 minutes.
Fixes#1611
This marks errors that are expected by a test with an "(Expected)"
marker and white color (instead of red).
The formatting of the log messages has been deferred to _render_log,
since the .expected attribute is not correctly set right after we read
the message.
