A bunch of boards failed the test with this error while running a DELTA update.
The AU failed and then the test crashed while trying to recover.

What happened:

AU started
2017/07/14 14:23:50.978 INFO |      auto_updater:0645| Waiting for update...status: UPDATE_STATUS_DOWNLOADING at progress 0.100379

Then when trying to get the next status it failed:
[0714/142400:INFO:update_engine_client.cc(493)] Querying Update Engine status...
[0714/142425:ERROR:object_proxy.cc(582)] Failed to call method: org.chromium.UpdateEngineInterface.GetStatus: object_path= /org/chromium/UpdateEngine: org.freedesktop.DBus.Error.NoReply: Did not receive a reply. Possible causes include: the remote application did not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or the network connection was broken.
[0714/142425:ERROR:dbus_method_invoker.h(111)] CallMethodAndBlockWithTimeout(...): Domain=dbus, Code=org.freedesktop.DBus.Error.NoReply, Message=Did not receive a reply. Possible causes include: the remote application did not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or the network connection was broken.
[0714/142425:ERROR:update_engine_client.cc(495)] Failed to query status

The exception was caught and RevertBootPartition was called to undo the update.

Then that crashed:
cmd=['ssh', '-p', '22', '-oConnectionAttempts=4', '-oUserKnownHostsFile=/dev/null', '-oProtocol=2', '-oConnectTimeout=30', '-oServerAliveCountMax=3', '-oStrictHostKeyChecking=no', '-oServerAliveInterval=10', '-oNumberOfPasswordPrompts=0', '-oIdentitiesOnly=yes', '-i', '/tmp/ssh-tmpuMqkd9/testing_rsa', 'root@chromeos4-row8-rack3-host1', '--', '/postinst', '/dev/sda5'], extra env={'LC_MESSAGES': 'C'}