Initial command-line support for cluster bring-up

Heavily WIP
I think it'd be easier if we extract out the command name from [`os.Args`](http://golang.org/pkg/os/) first and then call a different function in `main.go` depending on the command used. Then each command can have its own [`flag.FlagSet`](http://golang.org/pkg/flag/#FlagSet).

I did something similar in the `pie` project:

https://github.com/turingschool-examples/pie/blob/master/cmd/pie/main.go#L17-L44

The implementation could be cleaned up but the basic idea is there. Extract the command from the `os.Args`, pass remaining args to a command-specific function, then parse out the `flag.FlagSet` within there.

One thing we might want is a global `FlagSet` that has global flags that each command can use.