Add ability to assign additional keys to a user, add list-users and add-key commands.

[pirogoeth]

So I added the ability to add extra keys for a single user ID and the ability to list user IDs.

The list command looks like this:

→ sean@gamma | ~/.go/src/github.com/dcu/onetouch-ssh | SSH | branch: master | load: 0.10
λ onetouch-ssh list-users
        Authy ID        Key Comment                      Public Key
         3918644                                         b5:bd:c7:e1:f0:0f:2c:48:30:79:8c:1d:4c:af:f4:d4
         3918644        pirogoeth@eon.internal.maio.me   a7:8f:12:19:03:7c:8d:ab:24:1a:fe:43:23:f0:43:c0

And I've confirmed that add-key works. I know you removed ssh/user.go earlier today, but I've implemented a LoadUser command on top of the User struct that I was planning on incorporating into the list-users somehow. Maybe we can bring User struct and LoadUser into ssh/users_manager.go or just trim down ssh/user.go?

[pirogoeth]

Okay so this has very rapidly progressed from "add two things" to "ADD ALL THE THINGS".

I've trimmed some of the old database code from ssh/user.go, merged most (if not all) of the upstream changes, made some messages more concise, and added two more configuration options:

shell: <string>
shell_args: ["list", "of", "arguments"]

Use case: After login, the user gets dropped in to a bare bash shell because of the interactivity "hack", which completely skips any of the user's rcfiles, etc. So here's where it becomes useful:

shell: /bin/bash
shell_args: ["--login"]

... To basically re-enable launching the user's shell as a profile/login shell :)

Next, we probably need to definitely update the readme, enhance the error capturing/passing in utils.RunCommand, and maybe have a nice little progress spinner show up while waiting for the user's input from Authy (totally optional but would be pretty cool).

Note: I suppose this PR takes care of #11, #9, and #4...

[dcu]

we're missing a \n here

[dcu]

wow amazing work! thanks

[pirogoeth]

No problem! I'm enjoying toying around with this code and I really like the end-product, so it's kind-of a win-win 😆