kpod: info subcommand

Design: The output of the `info` subcommand ought to be directly
consumable in a format like JSON or yaml.
The structure being a map of sorts.

Each subsection of information being an individual cluster under the
top-level, like platform info, debug, storage, etc.

Even if there are errors under the top level key, the value will be a
map with the key of "error" and the value as the message of the
`err.Error()`. In this way, the command always returns usable output.

Ideally there will be a means for anything that can register info to do
so independently from it being in the single info.go, so this approach
is having a typed signature for the function that gives info, but i'm
sure it could be better.

Current iteration of this outputs the following as a limited user:

```yaml
host:
  MemFree: 711307264
  MemTotal: 2096222208
  SwapFree: 2147479552
  SwapTotal: 2147479552
  arch: amd64
  cpus: 1
  os: linux
store:
  error: 'mkdir /var/run/containers/storage: permission denied'

```

and as root (`sudo kpod info -D`):

```yaml
debug:
  compiler: gc
  go version: go1.7.6
  goroutines: 3
host:
  MemFree: 717795328
  MemTotal: 2096222208
  SwapFree: 2147479552
  SwapTotal: 2147479552
  arch: amd64
  cpus: 1
  os: linux
store:
  ContainerStore:
    number: 1
  GraphDriverName: overlay2
  GraphRoot: /var/lib/containers/storage
  ImageStore:
    number: 1
```

And with the `--json --debug` flag:

```json
{
  "debug": {
    "compiler": "gc",
    "go version": "go1.7.6",
    "goroutines": 3
  },
  "host": {
    "MemFree": 709402624,
    "MemTotal": 2096222208,
    "SwapFree": 2147479552,
    "SwapTotal": 2147479552,
    "arch": "amd64",
    "cpus": 1,
    "os": "linux"
  },
  "store": {
    "ContainerStore": {
      "number": 1
    },
    "GraphDriverName": "overlay2",
    "GraphRoot": "/var/lib/containers/storage",
    "ImageStore": {
      "number": 1
    }
  }
}
```

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

cmd/kpod/main.go

@@ -23,6 +23,7 @@ func main() {
 
 	app.Commands = []cli.Command{
 		imagesCommand,
+		infoCommand,
 		rmiCommand,
 		tagCommand,
 		versionCommand,