MFC: r343164

Clarify error messages a bit.

X-Found-With: r343112
Reviewed by: eugen (implicitly, when r343112 analysis)

MFC r343112: jail(8): stop crashing with SIGSEGV inside run_command()
function while processing not entirely correct jail.conf(5) file
having something like "ip4.addr = 127.0.0.1;" and no "ip4 = ...;"
so extrap variable stays NULL.

Reported by: marck

MFC r326276:

various: general adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

No functional change intended.

MFC r302856:

Fix up the order in which jail creation processes are run, to preserve
the config file's order in the non-parallel-start case.

PR: 209112
Approved by: re (gjb)