In Go unit tests, the entire test output becomes the failure message because
`go test` doesn't track why a test fails. This can make the failure message
pretty large, in particular in integration tests.
We cannot identify the real failure either because Kubernetes has no convention
for how to format test failures. What we can do is recognize log output added
by klog.
prune-junit-xml now moves the full text to to the test output and only keep
those lines in the failure which are not from klog.
The klog output parsing might eventually get moved to
k8s.io/logtools/logparse. For now it is developed as a sub-package of
prune-junit-xml.
