After the SDK Roll today (https://chromium-review.googlesource.com/c/chromium/src/+/1384104 )
net_unittests started failing in FYI bots with the following message:

2018-12-19 12:09:37,978:WARNING:root:Process exited with status code 255.
2018-12-19 12:09:37,978:INFO:root:Terminating kernel log reader.
Exception in thread Thread-87:
Traceback (most recent call last):
  File "/b/s/w/ir/.swarming_module/lib/python2.7/threading.py", line 801, in __bootstrap_inner
    self.run()
  File "/b/s/w/ir/build/util/lib/common/chrome_test_server_spawner.py", line 264, in run
    self.port_forwarder.Map(port_map)
  File "/b/s/w/ir/build/fuchsia/net_test_server.py", line 34, in Map
    common.ConnectPortForwardingTask(self._target, host_port)
  File "/b/s/w/ir/build/fuchsia/common.py", line 72, in ConnectPortForwardingTask
    output.returncode)
AttributeError: 'list' object has no attribute 'returncode'

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