Unix Socket Transport plugin causes a crash while under load

```
20-03-04 20:19:38.992 ERR arch_node_tasks.tasks.broadcast_forwarder.forwarder Unexpected main loop error:
Exception

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
File "/usr/lib/python3.7/site-packages/arch_node_tasks/tasks/broadcast_forwarder/forwarder.py", line 238, in main_loop
self._scan(hw.scan())
File "", line 2, in scan
File "/usr/lib/python3.7/site-packages/typedargs/utils.py", line 32, in _check_and_execute
retval = func(*convargs, **convkw)
File "/usr/lib/python3.7/site-packages/iotile/core/hw/hwmanager.py", line 764, in scan
devices = self.stream.scan(wait=wait)
File "/usr/lib/python3.7/site-packages/iotile/core/hw/transport/adapterstream.py", line 137, in scan
self._loop.run_coroutine(self.adapter.probe())
File "/usr/lib/python3.7/site-packages/iotile/core/utilities/async_tools/event_loop.py", line 536, in run_coroutine
return future.result()
File "/usr/lib/python3.7/concurrent/futures/_base.py", line 435, in result
return self.__get_result()
File "/usr/lib/python3.7/concurrent/futures/_base.py", line 384, in __get_result
raise self._exception
File "/usr/lib/python3.7/site-packages/iotile_transport_socket_lib/generic/device_adapter.py", line 78, in probe
await self._send_command(OPERATIONS.PROBE, None, COMMANDS.ProbeResponse)
File "/usr/lib/python3.7/site-packages/iotile_transport_socket_lib/generic/device_adapter.py", line 238, in _send_command
return await self.client.send_command(name, args, verifier, timeout=timeout)
File "/usr/lib/python3.7/site-packages/iotile_transport_socket_lib/generic/socket_client.py", line 137, in send_command
await self._implementation.send(packed)
File "/usr/lib/python3.7/site-packages/iotile_transport_socket_lib/unix_socket/unixsocket_implementation.py", line 117, in send
await self.con.send(encoded)
File "/usr/lib/python3.7/site-packages/iotile_transport_socket_lib/generic/abstract_socket_implementation.py", line 48, in send
raise ConnectionError from Exception
ConnectionError
20-03-04 20:19:39.028 DEB iotile.core.utilities.async_tools.event_loop Stopping task socket_client
20-03-04 20:19:39.030 ERR iotile.core.utilities.async_tools.event_loop object NoneType can't be used in 'await' expression
20-03-04 20:19:39.039 DEB transitions.core Initiating transition from state connected to state disconnected...
20-03-04 20:19:39.039 DEB transitions.core Exiting state connected. Processing callbacks...
20-03-04 20:19:39.040 INF transitions.core Exited state connected
20-03-04 20:19:39.040 DEB transitions.core Entering state disconnected. Processing callbacks...
20-03-04 20:19:39.041 INF transitions.core Entered state disconnected
20-03-04 20:19:41.048 DEB iotile.core.utilities.async_tools.event_loop Stopping task result=None>
20-03-04 20:19:41.049 DEB iotile.core.utilities.async_tools.event_loop Stopping task result=None>
20-03-04 20:19:41.051 DEB iotile.core.utilities.async_tools.event_loop Stopping task result=None>
20-03-04 20:19:41.052 DEB iotile.core.utilities.async_tools.event_loop Stopping task supervisor_client
20-03-04 20:19:41.053 DEB iotile.core.utilities.async_tools.event_loop Stopping task wait_for=()]>>
20-03-04 20:19:41.055 DEB iotile.core.utilities.async_tools.event_loop Stopping task result=None>
20-03-04 20:19:41.057 INF iotilegateway.supervisor.client Closing connection to server due to stop()
20-03-04 20:19:41.068 DEB iotile.core.utilities.async_tools.event_loop A task wasn't properly registered/cancelled as expected: wait_for= cb=[gather.._done_callback() at /usr/lib/python3.7/asyncio/tasks.py:691]>
20-03-04 20:19:41.069 DEB iotile.core.utilities.async_tools.event_loop A task wasn't properly registered/cancelled as expected: wait_for=<_GatheringFuture pending cb=[()]> cb=[_chain_future.._call_set_state() at /usr/lib/python3.7/asyncio/futures.py:355]>
20-03-04 20:19:41.070 DEB iotile.core.utilities.async_tools.event_loop A task wasn't properly registered/cancelled as expected: wait_for=>
20-03-04 20:19:41.074 ERR iotile.core.utilities.async_tools.event_loop Error stopping task >: CancelledError()
20-03-04 20:19:41.075 DEB iotile.core.utilities.async_tools.event_loop Finished loop in background thread
20-03-04 20:19:41.191 ERR asyncio Future exception was never retrieved
future:
concurrent.futures._base.CancelledError
sys:1: RuntimeWarning: coroutine 'wait_for' was never awaited
RuntimeWarning: Enable tracemalloc to get the object allocation traceback
root@arch-ap-002a:~#
[1] 0:bash*Z
```