LU-11394 utils: Adjust HOSTID constant

LU-11394 utils: Adjust HOSTID constant

Use constant defined in spl / post-0.8.0 libspl, for HOSTID file.
Also allows get_system_hostid() to be pulled in from ZFS 0.8.x

Lustre-change: https://review.whamcloud.com/34278
Lustre-commit: dce29976d14ca5aeba2dc8f0c464931c3826a6de

Test-Parameters: trivial
Signed-off-by: Nathaniel Clark <nclark@whamcloud.com>
Change-Id: Iba70d4f3b7f237260bdc964b28b601deeee81208
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/34654
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>