Better error handling when redis can't be reached

```
Process Process-1:
Traceback (most recent call last):
File "/usr/lib/python3.7/multiprocessing/process.py", line 297, in _bootstrap
self.run()
File "/usr/lib/python3.7/multiprocessing/process.py", line 99, in run
self._target(*self._args, **self._kwargs)
File "/home/rick/coco/coco/worker.py", line 86, in main_loop
loop.run_until_complete(go())
File "uvloop/loop.pyx", line 1451, in uvloop.loop.Loop.run_until_complete
File "/home/rick/coco/coco/worker.py", line 43, in go
conn = await aioredis.create_connection(("localhost", 6379), encoding="utf-8")
File "/usr/local/lib/python3.7/dist-packages/aioredis/connection.py", line 108, in create_connection
timeout, loop=loop)
File "/usr/lib/python3.7/asyncio/tasks.py", line 388, in wait_for
return await fut
File "/usr/local/lib/python3.7/dist-packages/aioredis/stream.py", line 19, in open_connection
lambda: protocol, host, port, **kwds)
File "uvloop/loop.pyx", line 1904, in create_connection
File "uvloop/loop.pyx", line 1883, in uvloop.loop.Loop.create_connection
ConnectionRefusedError: [Errno 111] Connection refused
```