camcontrol: Add a sense subcommand

As the name suggests, this sends a SCSI REQUEST SENSE to a device,
and prints out decoded sense information. It can also print out a
hexdump of the sense data.

sbin/camcontrol/camcontrol.c:
Add the new sense subcommand.

sbin/camcontrol/camcontrol.8:
Document camcontrol sense.

Sponsored by: Spectra Logic
Reviewed by: mav
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D43225