MFC r307182,307191,307192: rc.d/zfsbe: new script designed for BE support

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Make FILESYSTEMS, dumpon, and var not depend on zfs and zvol

Make zfs and zvol come before all of the items that depended on them
previously

MFC after: 2 weeks
Sponsored by: EMC / Isilon Storage Division

- Add descriptions to most of the rc scripts. Those are mostly taken from their
daemon's manpage and probably improved.
- Consistently use "filesystem" not "file system".

Approved by: bapt, brueffer
Differential Revision: D452

rc.d/zfs: pass -v option to zfs mount

this should make boot process more informative (and entertaining)
on systems with lots of zfs filesystems.

MFC after: 7 days

Currently there is a problem with fscking UFS file systems created on
top of ZVOLs. The problem is that rc.d/fsck runs before rc.d/zfs. The
latter makes ZVOLs to appear in /dev/. In such case rc.d/fsck cannot
find devfs entry and aborts. We cannot simply move rc.d/zfs before
rc.d/fsck, because we first want kern.hostid to be configured (by
rc.d/hostid). If we won't wait (hostid will be 0) we can reuse disks
which are in use by different systems (eg. in SAN/NAS environment).
We also cannot move rc.d/hostid before rc.d/fsck, because rc.d/hostid on
first system start stores generated kern.hostuuid in /etc/hostid file,
so it needs root file system to be mounted read-write.

The fix is to split rc.d/hostid so that rc.d/hostid (which will now run
before rc.d/fsck) only generates hostid and sets up sysctls, but doesn't
touch root file system and rc.d/hostid_save (which is run after
rc.d/root) and only creates /etc/hostid file.

With that in place, we can move ZVOL initialization to dedicated
rc.d/zvol script which runs before rc.d/fsck.

PR: conf/120194
Reported by: James Snow <snow@teardrop.org>
Reviewed by: brooks
Approved by: re (kib)
MFC after: 2 weeks

As previously discussed, add the svn:executable property to all scripts

Back out revision 1.6, the addition of "BEFORE: mountcritremote".

mountcritremote REQUIREs FILESYSTEMS, and that script REQUIREs zfs,
so this change is a noop. By removing it we make life a little easier
both for rcorder(8) and for debugging down the road.

Approved by: 2 weeks of silence from pjd

Be sure to run rc.d/zfs before mountcritremote. This way we can for example
configure devfs rules in /etc/devfs.conf for ZVOLs.

Submitted by: Yarema <yds@CoolRat.org>

When zfs dataset has jailed=on property, it won't be mounted with
'zfs mount -a' from the main system - this is by design, as mountpoint
may be set to dangerous value. This all means, that such file system
has to be mounted from within a jail. To make it easier, reorganize
rc.d/zfs script so it can be used from within a jail.

When org.freebsd:swap property is set to 'on' on a ZVOL, use is as a swap
device.

Discussed with: des

Remove the shutdown keyword. It just adds noise to the shutdown process.

- Create an empty /etc/zfs/exports file when zfs_enable="YES" and we don't
NFS-share anything. This way we can safely start mountd with
/etc/zfs/exports and mountd won't complain.

Pointed out by: ceri

- Move 'zfs volinit' before 'zfs mount -a' and 'zfs volfini' after
'zfs unmount -a'.

- Add ZFS startup script.

Submitted by: des

- When starting mountd(8) and ZFS is enabled, add /etc/zfs/exports file.
- Update rc.conf(5).