Docker: fix redis config, create /var/log/skynet

When I tried to run Skynet in Docker I got a few errors. With this patch I was able to run it.
- create /var/log/skynet
- in the config.js.docker (skynet config) match the redis settings to what the redis module expects.

Tested:
- build a new Docker image
- launch the image (docker run -i -t -p 3000 skynet:latest)
- create a new device in the localhost skynet
- use 'curl -X PUT' to update the device