todo: configure alternative docker storage drivers

[kayrus]

Put info here: https://coreos.com/os/docs/latest/customizing-docker.html or create new doc.

Write doc on how to configure custom storage driver for docker in CoreOS. Docs to read:
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Logical_Volume_Manager_Administration/thinly_provisioned_volume_creation.html
http://developerblog.redhat.com/2014/09/30/overview-storage-scalability-docker/
https://github.com/docker/docker/blob/master/daemon/graphdriver/devmapper/README.md
https://docs.docker.com/reference/commandline/daemon/#storage-driver-options
http://jpetazzo.github.io/2014/01/29/docker-device-mapper-resize/

Solve the problem:

/usr/bin/docker --daemon --debug --storage-driver 'devicemapper' --storage-opt 'dm.thinpooldev=/dev/VG/lvname'
...
FATA[0000] Shutting down daemon due to errors: error intializing graphdriver: EOF

[kbrwn]

There is a PR to make the EOF error more verbose moby/moby#16823 but it seems to be hit when the storage device isn't a properly configured thin-pool. I was able to set up this on CoreOS alpha (815.0.0) with docker 1.8.2

Wrote some rough docs on the process: https://gist.github.com/kbrwn/cebf471216a42cf71808
Now in markdown thanks to Josh Wood, https://gist.github.com/joshix/ec1673f2791bf5cb352f#file-thin-pool-md)

[reiz]

How ist the status of this?