Add node_hostkeys table to store ssh/sfs keys.
Add node_hostkeys table to store ssh/sfs keys.

* In dosfshostid, store sfs hostid into the new table. Fix sscanf that
  was not checking for a null argument. Check string for any slashes
  and reject it (since we use the id in a symlink call). Sanitize the
  string we insert into the db with mysql_escape_string().

* Fill out dokostkeys function stub that Mike added storing keys into
  the DB. If a key is not presented, it is set to NULL in the DB. This
  may not be the most desirable approach; we will find out. Note that
  I assume a node_hostkeys table entry already exists, and that I can
  just update it.

  Note that this function is kinda ugly; a perl regex library for C
  would be so nice!

nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome