* Add libadminmfs.pm with routines for entering/exiting and executing
  commands in, the admin MFS.  Node admin and firewall swapout (see
  below) now use this, the image creation process does not yet.

* Add swapout time hooks for running an admin mode process, likely to
  be used to collect swapout time state.  Currently controlled globally
  by two new sitevars.

* Modified node_admin to use the library and added a "-c <command>"
  option to have nodes go into admin mode and run a command.  I don't
  really expect this to be useful, it was just a testing vehicle for
  the library.

2. Improved the swapout process for firewalled experiments.  Largely
   just generalized what we already did for paniced experiments.
   At swapout, firewalled nodes are:

   - powered off
   - set to boot into admin mode and run a disk zapper
   - powered on

  The swapout process then waits for all nodes to successfully complete
  disk zapage, at which point the nodes are nfree'ed as usual....