client: Call "pk refresh" from checkout()
client: Call "pk refresh" from checkout()

- Update the hoard reference list on checkout, since we (may) have just
downloaded a new keyring

cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr