Add more payloads for nodejs.
* Adds a reverse and bind CMD payload
* Adds a bind payload (no bind_ssl for now).
Add missing require to nodejs/bind payload.
Move shared Node.js payload logic to mixin.
- this fixes the recursive loading issue when creating a payload
  inside the cmd payload
- also dries up some of the node cmd invocation logic.
Add SSL support to #nodejs_reverse_tcp.
Land #2508 - Add nodejs payloads