Truncating udev persistent net rules in remove-udev-persistent-rules.chroot hook rather than to remove them (Closes: #680763).

This allows to have non-persistent net devices with persistence properly,
see http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=680763#10 for more information.

share/hooks/008-remove-udev-persistent-rules.chroot

@@ -7,4 +7,10 @@ set -e
 # This removes udev persistent rules that cache the host systems mac address to
 # remember its device name.
 
-rm -f /etc/udev/rules.d/*persistent-net.rules
+for _FILE in /etc/udev/rules.d/*persistent-net.rules
+do
+	if [ -e "${_FILE}" ]
+	then
+		: > ${_FILE}
+	fi
+done