This save_index approach isn't perfect because getopt may skip
non-option arguments and they will be included in the help text:
$ build/storage-daemon/qemu-storage-daemon foo --object iothread
qemu-storage-daemon: foo --object iothread: Parameter 'id' is missing
$ build/storage-daemon/qemu-storage-daemon foo --object iothread,id=t
qemu-storage-daemon: --object iothread,id=t foo: Unexpected argument: foo
However, without changing the interface of loc_set_cmdline(), getting
the right index seems hard. Not sure what is the best way for fixing
this or if it's worth the effort.