We had devserver problems in the lab that killed a number of builds. These failures were all reported as test failures, not infrastructure. That's wrong.

Sample build:
https://uberchromegw.corp.google.com/i/chromeos/builders/peach_pit-paladin/builds/13206


Error from build logs:
03:41:07: WARNING: Exception is not retriable return code: 1; command: /b/cbuild/internal_master/chromite/third_party/swarming.client/swarming.py run --swarming chromeos-proxy.appspot.com --task-summary-json /tmp/cbuildbot-tmpZf1v6A/tmp_pM5Ne/temp_summary.json --raw-cmd --task-name peach_pit-paladin/R54-8676.0.0-rc1-bvt-cq --dimension os Ubuntu-14.04 --dimension pool default --print-status-updates --timeout 9000 --io-timeout 9000 --hard-timeout 9000 --expiration 1200 -- /usr/local/autotest/site_utils/run_suite.py --build peach_pit-paladin/R54-8676.0.0-rc1 --board peach_pit --suite_name suite_attr_wrapper --pool cq --num 6 --file_bugs False --priority CQ --timeout_mins 90 --retry True --max_retries 10 --minimum_duts 4 --offload_failures_only True --suite_args "{'attr_filter': '(suite:bvt-cq) and (subsystem:default)'}" -c
Priority was reset to 100
Triggered task: peach_pit-paladin/R54-8676.0.0-rc1-bvt-cq
chromeos-server31-172: 30731c2d71485810 1
  Autotest instance: cautotest
  08-05-2016 [03:41:02] Submitted create_suite_job rpc
  Error Message: StageControlFileFailure: Failed to stage peach_pit-paladin/R54-8676.0.0-rc1: staging artifacts=test_suites files=  for peach_pit-paladin/R54-8676.0.0-rc1 failed;HTTP OK not accompanied by 'Success'.
  Traceback (most recent call last):
    File "/usr/local/autotest/frontend/afe/json_rpc/serviceHandler.py", line 114, in dispatchRequest
      results['result'] = self.invokeServiceEndpoint(meth, args)
    File "/usr/local/autotest/frontend/afe/json_rpc/serviceHandler.py", line 154, in invokeServiceEndpoint
      return meth(*args)
    File "/usr/local/autotest/frontend/afe/rpc_handler.py", line 125, in new_fn
      return f(*args, **keyword_args)
    File "/usr/local/autotest/frontend/afe/rpc_utils.py", line 1336, in replacement
      return func(**kwargs)
    File "/usr/local/autotest/frontend/afe/site_rpc_interface.py", line 248, in create_suite_job
      test_source_build, hostname=sample_dut)
    File "/usr/local/autotest/frontend/afe/site_rpc_interface.py", line 143, in _stage_build_artifacts
      "Failed to stage %s: %s" % (build, e))
  StageControlFileFailure: Failed to stage peach_pit-paladin/R54-8676.0.0-rc1: staging artifacts=test_suites files=  for peach_pit-paladin/R54-8676.0.0-rc1 failed;HTTP OK not accompanied by 'Success'.
  
  Traceback (most recent call last):
    File "/usr/local/autotest/site_utils/run_suite.py", line 1737, in <module>
      sys.exit(main())
    File "/usr/local/autotest/site_utils/run_suite.py", line 1724, in main
      output_json = json.dumps(output_dict, sort_keys=True)
    File "/usr/lib/python2.7/json/__init__.py", line 250, in dumps
      sort_keys=sort_keys, **kw).encode(obj)
    File "/usr/lib/python2.7/json/encoder.py", line 209, in encode
      chunks = list(chunks)
    File "/usr/lib/python2.7/json/encoder.py", line 434, in _iterencode
      for chunk in _iterencode_dict(o, _current_indent_level):
    File "/usr/lib/python2.7/json/encoder.py", line 408, in _iterencode_dict
      for chunk in chunks:
    File "/usr/lib/python2.7/json/encoder.py", line 442, in _iterencode
      o = _default(o)
    File "/usr/lib/python2.7/json/encoder.py", line 184, in default
      raise TypeError(repr(o) + " is not JSON serializable")
  TypeError: JSONRPCException(u'StageControlFileFailure: Failed to stage peach_pit-paladin/R54-8676.0.0-rc1: staging artifacts=test_suites files=  for peach_pit-paladin/R54-8676.0.0-rc1 failed;HTTP OK not accompanied by \'Success\'.\nTraceback (most recent call last):\n  File "/usr/local/autotest/frontend/afe/json_rpc/serviceHandler.py", line 114, in dispatchRequest\n    results[\'result\'] = self.invokeServiceEndpoint(meth, args)\n  File "/usr/local/autotest/frontend/afe/json_rpc/serviceHandler.py", line 154, in invokeServiceEndpoint\n    return meth(*args)\n  File "/usr/local/autotest/frontend/afe/rpc_handler.py", line 125, in new_fn\n    return f(*args, **keyword_args)\n  File "/usr/local/autotest/frontend/afe/rpc_utils.py", line 1336, in replacement\n    return func(**kwargs)\n  File "/usr/local/autotest/frontend/afe/site_rpc_interface.py", line 248, in create_suite_job\n    test_source_build, hostname=sample_dut)\n  File "/usr/local/autotest/frontend/afe/site_rpc_interface.py", line 143, in _stage_build_artifacts\n    "Failed to stage %s: %s" % (build, e))\nStageControlFileFailure: Failed to stage peach_pit-paladin/R54-8676.0.0-rc1: staging artifacts=test_suites files=  for peach_pit-paladin/R54-8676.0.0-rc1 failed;HTTP OK not accompanied by \'Success\'.\n',) is not JSON serializable


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