User friendly recovery menu
---------------------------

Implements the spec in https://wiki.ubuntu.com/FriendlyRecovery

"Plugins" can be added easily:

* install a script in /lib/recovery-mode/options
* recovery-mode will invoke it with "test"
  - it should return "0" and print its name on stdout 
  - if it returns "1" here it will not be added to the 
    reovery-menu
* if the script is run with no parameters it should
  perform its action
* when the script is done, the menu is built again

