Safely set /etc/resolv.conf to an empty file in buildd images

In bionic buildd image chroot, /etc/resolv.conf is a symbolic link to
a configuration file in the /run directory. A call to truncate will
modify that file, which we should not do. Instead, we want to remove
the symbolic link and replace it with an empty file.

live-build/buildd/hooks/49-empty-resolv-conf.binary

@@ -1,4 +1,3 @@
-#!/bin/sh
+#!/bin/sh -e
-set -e
+chroot chroot rm /etc/resolv.conf
-
+chroot chroot touch /etc/resolv.conf
-chroot chroot truncate -s 0 /etc/resolv.conf