zfs-utils-lts: steal systemd service from upstream

zfs.service was removed from commit 16b015e, and
zfsonlinux/zfs@881f45c has not merged into 0.6.2 yet,
so there is no systemd service to start zfs on boot
currently. I steal some service files from the upstream,
and these files would be removed soon, hopefully.

Signed-off-by: Lance Chen <cyen0312@gmail.com>
Merge pull request #23 from Lance0312/lts-systemd-service

zfs-utils-lts: steal systemd service from upstream