rc.d: add a service jails config to all base system services

This gives more permissions to services (e.g. network access to
services which require this) when they are started as an automatic
service jail.

The sshd patch is important for the sshd-related functionality as
described in the man-page in the service jails part.

The location of the added env vars is supposed to allow overriding them
in rc.conf, and to hard-disable the use of svcj for some parts where it
doesn't make sense or will not work.

Only a subset of all of the services are fully tested (I'm running this
since more than a year with various services started as service jails).
The untested parts should be most of the time ok, in some edge-cases
more permissions are needed inside the service jail.
Differential Revision: https://reviews.freebsd.org/D40371

Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

rc.d: Fix NFS server startup scripts to enable vnet prison use

Now that commit cbbb22031f9b is in main,
it is possible to run nfsd(8), nfsuserd(8), mountd(8),
gssd(8) and rpc.tlsservd(8) in an appropriately configured vnet
prison if the "allow.nfsd" option is specified in jail.conf.

This patch fixes the rc scripts for this.
Mostly just replaces the "nojail" KEYWORD with "nojailvnet",
but also avoids setting vfs.nfsd.srvmaxio in a prison, since it
must be set outside of the prisons and applies to all
nfsd(8) instances.

Reviewed by: jamie
MFC after: 3 months
Differential Revision: https://reviews.freebsd.org/D38809

nfsd: Add a new rc variable nfs_server_maxio

Since vfs.nfsd.srvmaxio can only be set when nfsd.ko
is loaded, but nfsd is not running, setting it in
/etc/sysctl.conf is not feasible when "options NFSD"
was not specified for the kernel.

This patch adds a new rc variable nfs_server_maxio,
which sets vfs.nfsd.srvmaxio at the correct time.

rc.conf.5 will be patched separately.

Reviewed by: 0mp
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D32997

Add support for the new mountd -R option.

r376026 added a new "-R" option to mountd, which tells it to
not support the Mount protocol (not used by NFSv4) and not
register with rpcbind.
Rpcbind is considered a security issue by some sites now.

This patch adds a new yes/no variable called nfsv4_server_only.
When that is set, make vfs.nfsd.server_min_vers=4 and set "=R"
for mountd.
Setting vfs.nfsd.server_min_vers=4 tells nfsd to not register with rpcbind.
While here, add a check for "load_kld nfsd" failing to nfsd.

Reviewed by: 0mp
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D26938

Add support for a virtual hostname to nfsd

Specifically, this allows (via "-V vhostname") telling nfsd what principal
to use, instead of the hostname. This is used at iXsystems for fail-over in
HA systems.

Reviewed by: macklem
Sponsored by: iXsystems Inc.
Differential Revision: https://reviews.freebsd.org/D19191

Move the rc framework out of sbin/init into libexec/rc.

The reasons for this are forward looking to pkgbase:
* /sbin/init is a special binary; try not to replace it with
every package update because an rc script was touched.
(a follow-up commit will make init its own package)
* having rc in its own place will allow more easy replacement
of the rc framework with alternatives, such as openrc.

Discussed with: brd (during BSDCam), kmoore
Requested by: cem, bz
PR: 231522
Approved by: re (gjb)