Testrunner: Fix output parsing issue

Android build system determines failure info in the build log
by looking for a line starting with "FAILED: ".

The new format of the testrunner makes sure that the build system
is able to parse the error from the log.

Test: ./art/test.py -r -t 00
Change-Id: Iab29f254f600d4c3ee74cae2675da3a624e724ef
2 files changed