TBR: Continue suite if git diff fails

Commit log for first patchset:
---------------
Continue suite if git diff fails

Turns the failure of obtaining the diff for the test suite into a non-fatal
error, to handle failures on buildbots from mixed Cygwin and Windows paths.
---------------

[bruening, 2016-11-21 00:44:08]

Committed as
https://github.com/DynamoRIO/dynamorio/commit/a6658ad328664017ad982be9ecce0ca...

Final commit log: 
---------------
Continue suite if git diff fails

Turns the failure of obtaining the diff for the test suite into a non-fatal
error, to handle failures on buildbots from mixed Cygwin and Windows paths.

Review-URL: https://codereview.appspot.com/318830043
---------------

[bruening, 2016-11-21 01:54:03]

This gets the DR Cr Windows bots running tests again.  All tests pass but
the bot it still red: so there are more recipe problems left.
https://build.chromium.org/p/client.dynamorio/builders/win-7-dr/builds/1498/s...


On Sun, Nov 20, 2016 at 7:44 PM, <reply@codereview-hr.appspotmail.com>
wrote:

> Committed as
> https://github.com/DynamoRIO/dynamorio/commit/a6658ad3286640
> 17ad982be9ecce0cab112fb195
>
> Final commit log:
> ---------------
> Continue suite if git diff fails
>
> Turns the failure of obtaining the diff for the test suite into a
> non-fatal
> error, to handle failures on buildbots from mixed Cygwin and Windows
> paths.
>
> Review-URL: https://codereview.appspot.com/318830043
> ---------------
>
> http://codereview.appspot.com/318830043/
>
>
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