Add persistent drive support to Docker container

This works and runs containers now, if you eg `runc exec` into it.
Needs a few tweaks for rlimits, but will pull and run containers.

Will integrate better with ssh/dev containers to make more usable.

For a simple test use
```
./bin/moby build examples/docker.yml
./bin/moby run hyperkit -disk-size 100 docker

```

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

examples/docker.yml

@@ -0,0 +1,56 @@
+kernel:
+  image: "mobylinux/kernel:4.9.x"
+  cmdline: "console=ttyS0 console=tty0 page_poison=1"
+init: "mobylinux/init:c0007f0cdf1ef821a981fcc676e3f1c2dd9ab5b1"
+system:
+  - name: sysctl
+    image: "mobylinux/sysctl:2cf2f9d5b4d314ba1bfc22b2fe931924af666d8c"
+    net: host
+    pid: host
+    ipc: host
+    capabilities:
+     - CAP_SYS_ADMIN
+    readonly: true
+  - name: binfmt
+    image: "mobylinux/binfmt:bdb754f25a5d851b4f5f8d185a43dfcbb3c22d01"
+    binds:
+     - /proc/sys/fs/binfmt_misc:/binfmt_misc
+    readonly: true
+  - name: format
+    image: "mobylinux/format:53748000acf515549d398e6ae68545c26c0f3a2e"
+    binds:
+     - /dev:/dev
+    capabilities:
+     - CAP_SYS_ADMIN
+     - CAP_MKNOD
+daemon:
+  - name: rngd
+    image: "mobylinux/rngd:3dad6dd43270fa632ac031e99d1947f20b22eec9@sha256:1c93c1db7196f6f71f8e300bc1d15f0376dd18e8891c8789d77c8ff19f3a9a92"
+    capabilities:
+     - CAP_SYS_ADMIN
+    oomScoreAdj: -800
+    readonly: true
+  - name: dhcpcd
+    image: "mobylinux/dhcpcd:57a8ef29d3a910645b2b24c124f9ce9ef53ce703"
+    binds:
+     - /var:/var
+     - /tmp/etc:/etc
+    capabilities:
+     - CAP_NET_ADMIN
+     - CAP_NET_BIND_SERVICE
+     - CAP_NET_RAW
+    net: host
+    oomScoreAdj: -800
+  - name: docker
+    image: "mobylinux/docker-ce:f6505961df89ca6b5d024f1ac5a6b986359786d1"
+    capabilities:
+     - all
+    net: host
+    mounts:
+     - type: cgroup
+       options: ["rw","nosuid","noexec","nodev","relatime"]
+    binds:
+     - /dev:/dev
+     - /lib/modules:/lib/modules
+outputs:
+  - format: kernel+initrd