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/random: add support for zero harvest_mask

Replace the check for zero harvest_mask with new check for empty string.
This allows one to specify harvest_mask="0" that disables harversting
entropy from all but "pure" sources. Exact bit values for "pure" sources
differ for stable/12 and later branches, so it is handy to use zero.
The check for zero pre-dates introduction of "pure" non-maskable sources
Use empty string to disable altering sysctl kern.random.harvest.mask.

Note that notion of "pure" random sources is not documented in user level
manual pages yet. Still, it helps to extend battery life for hardware
with embedded "Intel Secure Key RNG" by disabling all other sources.

Note that no defaults changed and default behaviour is not affected.

Reported by: Dmitry Luhtionov

save-entropy(8), rc.d/random: Set nodump flag

Tag saved entropy files as "nodump," to signal that the files should not be
backed up by dump(8) or other automated backup software that honors the file
flag.

Do not produce an error if the target file resides on a filesystem that does
not support file flags (e.g., msdos /boot).

Reviewed by: delphij
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D20358

random(4): Attempt to persist entropy promptly

The goal of saving entropy in Fortuna is two-fold: (1) to provide early
availability of the random device (unblocking) on next boot; and (2), to
have known, high-quality entropy available for that initial seed. We know
it is high quality because it's output taken from Fortuna.

The FS&K paper makes it clear that Fortuna unblocks when enough bits have
been input that the output //may// be safely seeded. But they emphasize
that the quality of various entropy sources is unknown, and a saved entropy
file is essential for both availability and ensuring initial
unpredictability.

In FreeBSD we persist entropy using two mechanisms:

1. The /etc/rc.d/random shutdown() function, which is used for ordinary
shutdowns and reboots; and,

2. A cron job that runs every dozen minutes or so to persist new entropy, in
case the system suffers from power loss or a crash (bypassing the
ordinary shutdown path).

Filesystems are free to cache dirty data indefinitely, with arbitrary flush
policy. Fsync must be used to ensure the data is persisted, especially for
the cron job save-entropy, whose entire goal is power loss and crash safe
entropy persistence.

Ordinary shutdown may not need the fsync because unmount should flush out
the dirty entropy file shortly afterwards. But it is always possible power
loss or crash occurs during the short window after rc.d/random shutdown runs
and before the filesystem is unmounted, so the additional fsync there seems
harmless.

PR: 230876
Reviewed by: delphij, markj, markm
Approved by: secteam (delphij)
Differential Revision: https://reviews.freebsd.org/D19742

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)