Allow GEOM utilities to specify a -v option.

Geom utilities (geli(8), glabel(8), gmirror(8), gpart(8), gmirror(8),
gmountver(8), etc) all use the geom(8) utility as their back end
to process their commands and pass them into the kernel. Creating
a new utility requires no more than filling out a template describing
the commands and arguments that the utility supports. Consider the
specification for the very simple gmountver(8) utility:

struct g_command class_commands[] = {
{ "create", G_FLAG_VERBOSE | G_FLAG_LOADKLD, NULL,

	    {
		G_OPT_SENTINEL
	    },
	    "[-v] prov ..."

},
{ "destroy", G_FLAG_VERBOSE, NULL,

	    {
		{ 'f', "force", NULL, G_TYPE_BOOL },
		G_OPT_SENTINEL
	    },
	    "[-fv] name"

},
G_CMD_SENTINEL
};

It has just two commands of its own: "create" and "destroy" along
with the four standard commands "list", "status", "load", and
"unload" provided by the base geom(8) utility. The base geom(8)
utility allows each command to use the G_FLAG_VERBOSE flag to specify
that a command should accept the -v flag and when the -v flag is
given the utility prints "Done." if the command completes successfully.
In the above example, both of the commands set the G_FLAG_VERBOSE,
so have the -v option available. In addition the "destroy" command
accepts the -f boolean flag to force the destruction.

If the "destroy" command wanted to also print out verbose information,
it would need to explicitly declare its intent by adding a line:

		{ 'v', "verbose", NULL, G_TYPE_BOOL },

Before this change, the geom utility would silently ignore the above
line in the configuration file, so it was impossible for the utility
to know that the -v flag had been set on the command. With this
change a geom command can explicitly specify a -v option with a
line as given above and handle it as it would any other option. If
both a -v option and G_FLAG_VERBOSE are specified for a command
then both types of verbose information will be output when that
command is run with -v.

MFC after: 1 week
Sponsored by: Netflix