V8 Buildbot: Keep test-runner-exit-code control on the v8-side.
V8 Buildbot: Keep test-runner-exit-code control on the v8-side.

Clean up after https://codereview.chromium.org/1416373005/

The v8 test runner will now exit gracefully after test
failures. The infrastructure will still set step failures/
warnings accordingly.

Ignoring the test runner outcome completely was not very
clean as also internal exceptions were ignored, which led
to json parsing failures later.

Furthermore, this hack was only exercised on the
non-swarming tests.

BUG=chromium:535160

Review URL: https://codereview.chromium.org/1414043007

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@297433 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build