Improve error message of //tools/licenses.py.

Improve error message of //tools/licenses.py.

Current error message doesn't tell me which directory causes the error.

Review-Url: https://codereview.chromium.org/2802863004
Cr-Commit-Position: refs/heads/master@{#462791}
Committed: https://chromium.googlesource.com/chromium/src/+/32894e2ba3cd5d7a57d9160326d210205df7a861

[Hiroshi Ichikawa, 2017-04-06 04:58:12]

ichikawa@chromium.org changed reviewers:
+ phajdan.jr@chromium.org

[Paweł Hajdan Jr., 2017-04-06 11:52:44]

LGTM

[Hiroshi Ichikawa, 2017-04-07 01:48:11]

The CQ bit was checked by ichikawa@chromium.org

[commit-bot: I haz the power, 2017-04-07 01:48:38]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-04-07 06:10:18]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1491529691049550, "parent_rev":
"465fa2f3b877316159a8661723bf9a205e09dfe7", "commit_rev":
"32894e2ba3cd5d7a57d9160326d210205df7a861"}

[commit-bot: I haz the power, 2017-04-07 06:11:33]

Description was changed from

==========
Improve error message of //tools/licenses.py.

Current error message doesn't tell me which directory causes the error.
==========

to

==========
Improve error message of //tools/licenses.py.

Current error message doesn't tell me which directory causes the error.

Review-Url: https://codereview.chromium.org/2802863004
Cr-Commit-Position: refs/heads/master@{#462791}
Committed:
https://chromium.googlesource.com/chromium/src/+/32894e2ba3cd5d7a57d9160326d2...
==========

[commit-bot: I haz the power, 2017-04-07 06:11:34]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/32894e2ba3cd5d7a57d9160326d2...