cli: change argument parsing convention for subcommands

cli: change argument parsing convention for subcommands

previously we deleted the subcommand name from argv before passing to
the subcommand. In this version, the deletion is done in the actual
subcommands. Although this causes some duplication of code, it allows
us to be more flexible about how we parse command line arguments in
the subcommand, including possibly using off-the-shelf routines like
getopt_long that expect the name of the command in argv[0].