Allow Docker to configure direct-lvm mode

[dforste]

https://docs.docker.com/engine/userguide/storagedriver/device-mapper-driver/#configure-direct-lvm-mode-for-production

In Docker 17.06 and higher, Docker can manage the block device for you, simplifying configuration of direct-lvm mode.

They now have options to simply pass in dm.directlvm_device="/dev/xvdf" to allow docker to configure the raw device.

The full example is

  "storage-driver": "devicemapper",
  "storage-opts": [
    "dm.directlvm_device=/dev/xdf",
    "dm.thinp_percent=95",
    "dm.thinp_metapercent=1",
    "dm.thinp_autoextend_threshold=80",
    "dm.thinp_autoextend_percent=20",
    "dm.directlvm_device_force=false"
  ]
}```