LUDOC-56 zfs: discuss ZFS in parts of the manual

LUDOC-56 zfs: discuss ZFS in parts of the manual

Added ZFS filesystem limits in the Lustre limits tables, since they
are significantly different from ldiskfs filesystem limits.

Include mention of ZFS in a few key places.  This definitely is
just a starting point, since a full discussion of formatting and
maintaining ZFS is needed in the manual.

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Richard Henwood <richard.henwood@intel.com>
Change-Id: Icaea5657e43ec58466f4ea8047fbec65b2805701
Reviewed-on: http://review.whamcloud.com/9740
Tested-by: Jenkins