Fix asymmetry of JUnit notifier invocations on failed steps.

The JUnit Notifier.fireTestFinished will also be called when a step fails.
This symmetry allows gradle to detect failed steps.
Without the invocation gradle ignores test failures and marks the build
as successful.

Peter Niederwiesers answer: http://forums.gradle.org/gradle/topics/with_custom_junit_runner_failures_are_ignored