Allow rc.d script to provide "status" method, even if it does not

define procname or have a PID file. This might be useful for cases,
such as mounting local FS, when there is no running daemon
still some other persistent state in the system which status
can be checked.

It is still possible to have a status method before this by having
extra_commands="status", but it's not obvious and might give
an script writer some extra legwork to figure out how and why
the straight method is not working.

Reviewed by:	cy
MFC after:	1 week
Relnotes:	yes
Differential Revision:	https://reviews.freebsd.org/D31614

libexec/rc/rc.subr

@@ -958,6 +958,11 @@ run_rc_command()
 			_pidcmd='rc_pid=$(check_process '"$_procname $command_interpreter"')'
 		fi
 		_keywords="${_keywords} status poll"
+	else
+		if [ ! -z "${status_cmd}" ]
+		then
+			_keywords="${_keywords} status"
+		fi
 	fi
 
 	if [ -z "$rc_arg" ]; then