[FEATURE REQUEST] Display 'drained' nodes

We have our mangers configured to 'drained' so they don't run containers automatically. It would be good if we could grey them out or somehow show that they are drained. 
`docker node update --availability drain <NODE>`

The setting is readable in the `docker node inspect` command json, so would be good to expose that.

Thanks, 
PS. Loving this project so far