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/

Introduce startmsg and use it in rc scripts

startmsg is a new rc.subr(8) function function to be used instead of
echo(1) when for boot messages. It replaces the often forgotten

check_startmsgs && echo ...

with

startmsg ...

No functional change intended.

I adjusted the commit message and did some final clean-ups of the patch
before committing.

PR: 255207
Reported by: Jose Luis Duran <jlduran@gmail.com>
Reviewed by: imp, 0mp
Approved by: imp (src)
Differential Revision: https://reviews.freebsd.org/D34514

pf: fallback if $pf_rules fails to load

Support loading a default pf ruleset in case of invalid pf.conf.

If no pf rules are loaded pf will pass/allow all traffic, assuming the
kernel is compiled without PF_DEFAULT_TO_DROP, as is the case in
GENERIC.

In other words: if there's a typo in the main pf_rules we would allow
all traffic. The new default rules minimise the impact of this.

If $pf_program (i.e. pfctl) fails to set $pf_fules and
$pf_fallback_rules_enable is YES we will load $pf_fallback_rules_file if
set, or $pf_fallback_rules.

$pf_fallback_rules can include multiple rules, for example to permit
traffic on a management interface.

$pf_fallback_rules_enable defaults to "NO", preserving historic behaviour.

man page changes by ceri@.

PR: 256410
Reviewed by: donner, kp
Sponsored by: semaphor.dk
Differential Revision: https://reviews.freebsd.org/D30791

[pf] /etc/rc.d/pf should REQUIRE routing

When a system with pf_enable="YES" in /etc/rc.conf uses hostnames in
/etc/pf.conf, these hostnames cannot be resolved via external nameservers
because the default route is not yet set. This results in an empty
(all open) ruleset.

Since r195026 already put netif back to REQUIRE, this change does not affect
the issue that the firewall should rather have been setup before any
network traffic can occur.

PR: 211928
Submitted by: Robert Schulze
Reported by: Robert Schulze
Tested by: Mateusz Kwiatkowski
No objections from: kp
MFC after: 3 days

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)