LU-8694 docs: ZFS hostid mkfs.lustre(8) man page update

LU-8694 docs: ZFS hostid mkfs.lustre(8) man page update

Add note about needing to reload spl module after creating /etc/hostid
file.

Test-Parameters: trivial
Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Change-Id: Ie4c3697567ed2722742324fd70f382bb46a886d6
Reviewed-on: http://review.whamcloud.com/23118
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Steve Guminski <stephenx.guminski@intel.com>
Reviewed-by: Cliff White <cliff.white@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>