[swarming] Add luci-go's isolate tool, downloaded via runhooks.

[swarming] Add luci-go's isolate tool, downloaded via runhooks.

Port https://codereview.chromium.org/1154633003/

BUG=chromium:535160
LOG=n

Committed: https://crrev.com/baeb9125e1d9f9ba560bd21a741e1aca927082b3
Cr-Commit-Position: refs/heads/master@{#31045}

[Michael Achenbach, 2015-10-01 07:23:49]

machenbach@chromium.org changed reviewers:
+ jochen@chromium.org, tandrii@chromium.org

[Michael Achenbach, 2015-10-01 07:24:27]

PTAL

[Michael Achenbach, 2015-10-01 07:41:37]

The CQ bit was checked by machenbach@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-10-01 07:41:44]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1380983002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1380983002/1

[commit-bot: I haz the power, 2015-10-01 07:45:57]

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

[commit-bot: I haz the power, 2015-10-01 07:45:58]

Dry run: Try jobs failed on following builders:
  v8_presubmit on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_presubmit/builds/6249)

[M-A Ruel, 2015-10-01 12:06:59]

maruel@chromium.org changed reviewers:
+ maruel@chromium.org

[M-A Ruel, 2015-10-01 12:06:59]

Note that this is semi problematic, as we roll semi-frequently and often these
rolls are time sensitive.

I'll try to come up with an idea (likely embedding this at the recipe level, not
in the repository, since this is infrastructure) but lgtm for short term to get
this going.

[Michael Achenbach, 2015-10-01 12:09:28]

On 2015/10/01 12:06:59, M-A Ruel wrote:
> Note that this is semi problematic, as we roll semi-frequently and often these
> rolls are time sensitive.
> 
> I'll try to come up with an idea (likely embedding this at the recipe level,
not
> in the repository, since this is infrastructure) but lgtm for short term to
get
> this going.

We could also move this into the buildtools repo.

[Michael Achenbach, 2015-10-01 12:09:32]

The CQ bit was checked by machenbach@chromium.org

[commit-bot: I haz the power, 2015-10-01 12:09:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1380983002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1380983002/1

[commit-bot: I haz the power, 2015-10-01 12:11:36]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-01 12:11:57]

Patchset 1 (id:??) landed as
https://crrev.com/baeb9125e1d9f9ba560bd21a741e1aca927082b3
Cr-Commit-Position: refs/heads/master@{#31045}