Changes to nfree in how scheduled reloads are handled. Instead of
firing off an os_load, just move the node from its current reservation to emulab-ops/reloadpending. This moves the operation out of band from the user's perspective (he gets more immediate response when an experiment ends, and besides we cannot handle mass reloads anyway, and so this approach is unusable until Frisbee. Change the reload_daemon to look for free nodes that need a reload (as before) *and* nodes in emulab-ops/reloadpending (as put there by nfree). In this case, the imageid comes from the reloads table instead of the node-types table. I also updated the reload_daemon to use libdb routines. Also change testbed/reloading to emulab-ops/reloading. Maybe someday I'll remove these hardwired strings.