• Add CSV output to gstat via -C flag.

Add a -C option, similar to -B, that allows gstat to produce basic CSV output
with absolute timestamps (ISO 8601, nearly.) Multiple devices are handled by
way of a single-pivot CSV table with duplicated timestamps for each object
output.

Submitted by: Nick Principe <nap__ixsystems.com>
Reviewed by: myself, imp@, asomers (earlier verison), bcr (manpages)
Sponsored by: iXsystems Inc.
Differential Revision: https://reviews.freebsd.org/D16151