Filing to track if it recurs.

https://luci-milo.appspot.com/buildbot/chromeos/stout-paladin/22905

upload_prebuilts: Unhandled exception:
Traceback (most recent call last):
  File "/b/c/cbuild/repository/chromite/bin/upload_prebuilts", line 168, in <module>
    DoMain()
  File "/b/c/cbuild/repository/chromite/bin/upload_prebuilts", line 164, in DoMain
    commandline.ScriptWrapperMain(FindTarget)
  File "/b/c/cbuild/repository/chromite/lib/commandline.py", line 837, in ScriptWrapperMain
    ret = target(argv[1:])
  File "/b/c/cbuild/repository/chromite/scripts/upload_prebuilts.py", line 880, in main
    options.toolchain_upload_path)
  File "/b/c/cbuild/repository/chromite/scripts/upload_prebuilts.py", line 631, in SyncBoardPrebuilts
    self._UploadPrebuilt(package_path, packages_url_suffix)
  File "/b/c/cbuild/repository/chromite/scripts/upload_prebuilts.py", line 455, in _UploadPrebuilt
    RemoteUpload(self._gs_context, self._acl, upload_files)
  File "/b/c/cbuild/repository/chromite/scripts/upload_prebuilts.py", line 234, in RemoteUpload
    parallel.RunTasksInProcessPool(upload, tasks, pool)
  File "/b/c/cbuild/repository/chromite/lib/parallel.py", line 809, in RunTasksInProcessPool
    queue.put((idx, input_args))
  File "/usr/lib/python2.7/contextlib.py", line 24, in __exit__
    self.gen.next()
  File "/b/c/cbuild/repository/chromite/lib/parallel.py", line 750, in BackgroundTaskRunner
    queue.put(_AllTasksComplete())
  File "/b/c/cbuild/repository/chromite/lib/parallel.py", line 750, in BackgroundTaskRunner
    queue.put(_AllTasksComplete())
  File "/usr/lib/python2.7/contextlib.py", line 24, in __exit__
    self.gen.next()
  File "/b/c/cbuild/repository/chromite/lib/parallel.py", line 561, in ParallelTasks
    raise BackgroundFailure(exc_infos=errors)
chromite.lib.parallel.BackgroundFailure: <class 'chromite.lib.gs.GSNoSuchKey'>: return code: 1; command: /b/c/cbuild/repository/.cache/common/gsutil_4.19.tar.gz/gsutil/gsutil -o 'Boto:num_retries=10' -h x-goog-if-generation-match:0 cp -v -- /b/c/cbuild/repository/chroot/build/stout/packages/dev-only-extras.tbz2 gs://chromeos-prebuilt/board/stout/paladin-R61-9719.0.0-rc3/packages/dev-only-extras.tbz2
CommandException: No URLs matched: /b/c/cbuild/repository/chroot/build/stout/packages/dev-only-extras.tbz2