sbin: Automated cleanup of cdefs and other formatting

Apply the following automated changes to try to eliminate
no-longer-needed sys/cdefs.h includes as well as now-empty
blank lines in a row.

Remove /^#if.*\n#endif.*\n#include\s+<sys/cdefs.h>.*\n/
Remove /\n+#include\s+<sys/cdefs.h>.*\n+#if.*\n#endif.*\n+/
Remove /\n+#if.*\n#endif.*\n+/
Remove /^#if.*\n#endif.*\n/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/types.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/param.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/capsicum.h>/

Sponsored by: Netflix

Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

Make use of the getlocalbase() function for run-time adjustment of the
local software base directory, as committed in SVN rev. 367813.

The pkg and mailwrapper programs used the LOCALBASE environment variable
for this purpose and this functionality is preserved by getlocalbase().

After this change, the value of the user.localbase sysctl variable is used
if present (and not overridden in the environment).

The nvmecontrol program gains support of a dynamic path to its plugin
directory with this update.

Differential Revision: https://reviews.freebsd.org/D27237

Revert the whole getlocalbase() set of changes while a different design is
hashed out.

Replace hardcoded references to _PATH_LOCALBASE with calls to getlocalbase.3

Reviewed by: imp, se

Improve nvmecontrol error reporting.

MFC after: 1 week
Sponsored by: iXsystems, Inc.

Assume all the short args have optional args so allocate space for the
':'. It's slightly wasteful, but much easier (and the savings in bytes
at runtime would be tiny, but the code to do it larger).

Submitted by: Sebastian Huber

Fix usage printing for nested subcommands.

Instead of `nvmecontrol create` should be `nvmecontrol ns create`, etc.

MFC after: 2 weeks

Fix several related coverity issues:

Make sure to always free shortopts and lopts when returning.
Fix minor logic bug to guard against NULLs properly.

CID: 1403654, 1403656, 1403658

Create generic command / arg parsing routines

Create a set of routines and structures to hold the data for the args
for a command. Use them to generate help and to parse args. Convert
all the current commands over to the new format. "comnd" is a hat-tip
to the TOPS-20 %COMND JSYS that (very) loosely inspired much of the
subsequent command line notions in the industry, but this is far
simpler (the %COMND man page is longer than this code) and not in the
kernel... Also, it implements today's de-facto
command [verb]+ [opts]* [args]*
format rather than the old, archaic TOPS-20 command format :)

This is a snapshot of a work in progress to get the nvme passthru
stuff committed. In time it will become a private library and used
by some other programs in the tree that conform to the above pattern.

Differential Revision: https://reviews.freebsd.org/D19296