Make webkit-patch auto-rebaseline a bit more robust to errors.

Make webkit-patch auto-rebaseline a bit more robust to errors.

This logs errors when the underlying commands fail, and tries
to recover a bit more cleanly.

TBR=eseidel@chromium.org, ojan@chromium.org, wangxianzhu@chromium.org
BUG=397678
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=179877

[Xianzhu, 2014-07-25 22:10:45]

lgtm.

[Dirk Pranke, 2014-07-29 18:23:01]

The CQ bit was checked by dpranke@chromium.org

[commit-bot: I haz the power, 2014-07-29 18:24:14]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/dpranke@chromium.org/417123006/1

[commit-bot: I haz the power, 2014-07-29 20:00:16]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_blink_dbg on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/linux_blink_dbg/builds/1...)
  linux_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/linux_blink_rel/builds/1...)
  mac_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/mac_blink_rel/builds/17573)

[commit-bot: I haz the power, 2014-07-29 20:07:34]

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

[commit-bot: I haz the power, 2014-07-29 20:07:35]

Try jobs failed on following builders:
  linux_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/linux_blink_rel/builds/1...)
  mac_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/mac_blink_rel/builds/17581)

[Dirk Pranke, 2014-08-08 20:58:56]

The CQ bit was checked by dpranke@chromium.org

[commit-bot: I haz the power, 2014-08-08 20:59:59]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/dpranke@chromium.org/417123006/1

[commit-bot: I haz the power, 2014-08-08 21:08:51]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_blink_dbg on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/linux_blink_dbg/builds/2...)
  linux_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/linux_blink_rel/builds/1...)
  mac_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/mac_blink_rel/builds/19089)

[commit-bot: I haz the power, 2014-08-08 21:15:17]

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

[commit-bot: I haz the power, 2014-08-08 21:15:18]

Try jobs failed on following builders:
  mac_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/mac_blink_rel/builds/19090)

[Dirk Pranke, 2014-08-08 21:51:04]

The CQ bit was checked by dpranke@chromium.org

[commit-bot: I haz the power, 2014-08-08 21:52:03]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/dpranke@chromium.org/417123006/20001

[commit-bot: I haz the power, 2014-08-08 23:28:02]

Change committed as 179877