tools/disktool: Rename some command-line parameters
tools/disktool: Rename some command-line parameters

- Rename -h/--hdk to -d/--directory and update help text, since it doesn't
actually want the hdkdir but its parent

- Change --chunksperdir from -d to -m

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