Fix zpool subcommands error message with some unsupported options

Fix zpool subcommands error message with some unsupported options

Both 'detach' and 'online' zpool subcommands, when provided with an
unsupported option, forget to print it in the error message:

   # zpool online -t rpool vda3
   invalid option ''
   usage:
      online [-e] <pool> <device> ...

This changes fixes the error message in order to include the actual
option that is not supported.

Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #9270