"reserve" will automatically approve sufficiently small reservation
requests.  Otherwise, it will make a note in the database but not actually
hold any resources.  Big reservation requests can be approved manually,
with the "reserve -a" option (either at the time of the initial request,
or subsequently with "reserve -a -m ...").

When a reservation request is feasible but not auto-approved, "reserve"
will send e-mail to testbed-ops and exit with status 2.