[Telemetry] Fix exception handling in user story runner.

[Telemetry] Fix exception handling in user story runner.

Currently, unrecoverable exception raised during a user story run does not
create a failure value for that user story. This leads to confusing log output
by gtest_progress_reporter.

This patch fixes this by catching unrecoverable exception and add failure value
to the currently user story value. This patch also improve unittest in
user_story_runner_unittest to make sure that the stdout output captures the
raise exceptions.

BUG=448827
Committed: https://crrev.com/326b32902255707e5a4154ed4db10f46c9fc8905
Cr-Commit-Position: refs/heads/master@{#313161}

[nednguyen, 2015-01-26 18:15:55]

Patchset #1 (id:1) has been deleted

[nednguyen, 2015-01-26 18:17:10]

nednguyen@google.com changed reviewers:
+ aiolos@chromium.org, slamm@chromium.org, sullivan@chromium.org

[slamm, 2015-01-26 18:22:23]

lgtm

[sullivan, 2015-01-26 18:24:17]

The CQ bit was checked by sullivan@chromium.org

[sullivan, 2015-01-26 18:24:18]

lgtm

[commit-bot: I haz the power, 2015-01-26 18:24:55]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/875993002/20001

[commit-bot: I haz the power, 2015-01-26 19:25:08]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-01-26 19:25:09]

Try jobs failed on following builders:
  mac_chromium_rel_ng on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[nednguyen, 2015-01-26 19:27:19]

The CQ bit was checked by nednguyen@google.com

[commit-bot: I haz the power, 2015-01-26 19:28:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/875993002/20001

[commit-bot: I haz the power, 2015-01-26 19:28:54]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-01-26 19:28:55]

Try jobs failed on following builders:
  mac_chromium_rel_ng on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[nednguyen, 2015-01-26 19:32:43]

The CQ bit was checked by nednguyen@google.com

[commit-bot: I haz the power, 2015-01-26 19:34:06]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/875993002/20001

[commit-bot: I haz the power, 2015-01-26 20:37:49]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-01-26 20:37:50]

Try jobs failed on following builders:
  mac_chromium_rel_ng on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[nednguyen, 2015-01-26 22:01:54]

The CQ bit was checked by nednguyen@google.com

[commit-bot: I haz the power, 2015-01-26 22:02:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/875993002/40001

[commit-bot: I haz the power, 2015-01-26 22:58:32]

Committed patchset #2 (id:40001)

[commit-bot: I haz the power, 2015-01-26 22:59:34]

Patchset 2 (id:??) landed as
https://crrev.com/326b32902255707e5a4154ed4db10f46c9fc8905
Cr-Commit-Position: refs/heads/master@{#313161}