Refactor --with-sysconfig, default to /etc/default and /etc/conf.d

Both Debian and Builroot based systems use /etc/default and
Alpine Linux use /etc/conf.d, so let's just put both in by
default.  If the directories exist we monitor them.

The --with-syconfig configure option is now disabled by default.

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

contrib/debian/build.sh

@@ -27,7 +27,7 @@ echo
     --enable-dbus-plugin              --enable-x11-common-plugin	\
     --enable-alsa-utils-plugin						\
     --with-random-seed=/var/lib/urandom/random-seed			\
-    --with-heading="Debian GNU/Linux" --with-hostname="stretch"
+    --with-heading="Debian GNU/Linux"
 
 if [ $? -ne 0 ]; then
     echo