The servers package, and router.go in particular, had become quite
large. Address this by moving some things out to separate packages:
* http request handlers all move to pkg/server/handlers.
* node password bootstrap auth handler goes into pkg/nodepassword with
  the other nodepassword code.

While we're at it, also be more consistent about calling variables that
hold a config.Control struct or reference `control` instead of `config` or `server`.
Signed-off-by: Brad Davidson <brad.davidson@rancher.com>