Let test driver fail if test executable can't list the tests.

TBR=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/605133004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24253 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

tools/testrunner/local/testsuite.py

@@ -234,7 +234,7 @@ class GoogleTestSuite(TestSuite):
     if output.exit_code != 0:
       print output.stdout
       print output.stderr
-      return []
+      raise Exception("Test executable failed to list the tests.")
     tests = []
     test_case = ''
     for line in output.stdout.splitlines():