Add support for SysV-only scripts in runparts

This patch extens the SysV compatibility support in Finit by adding
support for limiting `runparts` to run only SNNfoo, or KNNfoo, style
scripts from a directory.

Additionally, by default `runparts` now runs entirely in the background
without any progress.  To enable progress, an optional argument has been
added to the runparts command line.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

test/skel/etc/rcS.d/S01abc.sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+echo "$0 $*" >> /tmp/sysv.log

test/skel/etc/rcS.d/S02def.sh

@@ -0,0 +1 @@
+S01abc.sh

test/skel/etc/rcS.d/foo.sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+echo "$0" >> /tmp/sysv.log

test/skel/etc/rcS.d/test.sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+echo "$0" >> /tmp/sysv.log