[Metrics] Fix presubmit scripts to return an error code on failure.

[Metrics] Fix presubmit scripts to set an error exit code on failure.

Due to a bug in a recent refactoring, the script would log an error to the
console, but would still set the success exit code, 0.

BUG=468523
TEST=Try to submit a CL with invalid formatting, the presubmit script should block submission.
R=asvitkine@chromium.org

Committed: https://crrev.com/385bc2ca9d49328c27f1af967b16439acaa44817
Cr-Commit-Position: refs/heads/master@{#321436}

[Ilya Sherman, 2015-03-18 23:11:22]

isherman@chromium.org changed reviewers:
+ mpearson@chromium.org

[Mark P, 2015-03-19 18:52:41]

lgtm

[Ilya Sherman, 2015-03-19 21:15:11]

The CQ bit was checked by isherman@chromium.org

[commit-bot: I haz the power, 2015-03-19 21:19:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1019123003/10005

[commit-bot: I haz the power, 2015-03-19 21:43:02]

Committed patchset #2 (id:10005)

[commit-bot: I haz the power, 2015-03-19 21:43:56]

Patchset 2 (id:??) landed as
https://crrev.com/385bc2ca9d49328c27f1af967b16439acaa44817
Cr-Commit-Position: refs/heads/master@{#321436}