[Bug 228066] Jail hook missing between launch and exec.start

[b***@freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=228066

--- Comment #2 from commit-***@freebsd.org ---
A commit references this bug:

Author: netchild
Date: Wed Aug 15 18:35:43 UTC 2018
New revision: 337863
URL: https://svnweb.freebsd.org/changeset/base/337863

Log:
- Add exec hook "exec.created". This is called when the jail is
created and before exec.start is called. [1]
- Bump __FreeBSD_version.

This allows to attach ZFS datasets and various other things to be
done before any command/service/rc-script is started in the new
jail.

PR: 228066 [1]
Reviewed by: jamie [1]
Submitted by: Stefan Gr?nke <***@gronke.net> [1]
Differential Revision: https://reviews.freebsd.org/D15330 [1]

Changes:
head/sys/sys/param.h
head/usr.sbin/jail/command.c
head/usr.sbin/jail/config.c
head/usr.sbin/jail/jail.8
head/usr.sbin/jail/jail.c
head/usr.sbin/jail/jailp.h