Fix for local homedirs getting left as owned by root.
See emulab-devel issue 227 for details. Also, on a "reset" clean out the correct BDB files. It has been a long time since they used ".db" as the suffix. Now there are ".pag" and ".dir" files. We haven't noticed because we don't really use the "reset" operation. The prepare script just removes everything in /var/emulab/db.