new remctl command "install" to invoke autoinstaller

e.g.,
  $ remctl black-mesa control moobarspam install etch /path/to/rootpasshash

The root password to be used is taken from a given file local to black-mesa...
probably this should be in the database or something, randomly generated
by the web interface, and available for reminders.

svn path=/trunk/packages/sipb-xen-database/sipb-xen-database/; revision=223