client: Check hoard cache for keyring when hoarding
client: Check hoard cache for keyring when hoarding

- Precalculate the base path of hoard cache image files in
parse_parcelcfg(), rather than doing it in checkout()

- When hoarding a parcel that isn't checked out, check the hoard cache
for the keyring before downloading it

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