Bots are purple with the following error message "shard #0 had an internal swarming failure".

See for example https://uberchromegw.corp.google.com/i/internal.bling.main/builders/smoke/builds/19489

When clicking on the link, we see that the bot have failed with the following python error:

8846 2017-12-07 04:29:47.833 E: internal failure: Could not install packages; exit code -9
output:
Traceback (most recent call last):
  File "/b/swarm_slave/swarming_bot.1.zip/client/run_isolated.py", line 590, in map_and_run
    with install_packages_fn(run_dir) as cipd_info:
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/contextlib.py", line 17, in __enter__
    return self.gen.next()
  File "/b/swarm_slave/swarming_bot.1.zip/client/run_isolated.py", line 930, in install_client_and_packages
    run_dir, cipd_cache_dir, client, packages, timeoutfn())
  File "/b/swarm_slave/swarming_bot.1.zip/client/run_isolated.py", line 859, in _install_packages
    timeout=timeout,
  File "/b/swarm_slave/swarming_bot.1.zip/client/cipd.py", line 219, in ensure
    exit_code, '\n'.join(output)))
Error: Could not install packages; exit code -9
output:
Sending the crash report ... done.
Report URL: https://touch-isolate.appspot.com/restricted/ereporter2/errors/5641647580774400
Could not install packages; exit code -9
output: