Roll src/tools/swarming_client/ to 8786f2b007a6df8e6e7a85e61d8b7928d408ffa1.
Roll src/tools/swarming_client/ to 8786f2b007a6df8e6e7a85e61d8b7928d408ffa1.

$ git log 1d87b2fd3..8786f2b00 --date=short --format='%ad %ae %s'
2015-09-18 maruel Fix crash when the task expired.
2015-09-17 maruel Trap the exception sooner when a download from GCS fails.
2015-09-17 maruel Update third_party_local/depot_tools and add subprocess42.Popen.popen_lock.
2015-09-17 maruel Use deterministic tree location instead of random names.
2015-09-16 maruel Fix swarming.py collect when there was no try.
2015-09-16 maruel Always check for presence before calling rmtree().
2015-09-16 maruel Fallbacks hardlinks to copy transparently.

R=vadimsh@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1353583003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#349684}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk