Improve the dns handling

Somehow the OS image comes with the line
dns =

which is not valid and will not be replaced.

Change-Id: Ia37217f493a1451d7691424e004e2625a460dac4
diff --git a/playbooks/roles/configure-targethosts/tasks/configure-network-Debian.yml b/playbooks/roles/configure-targethosts/tasks/configure-network-Debian.yml
index 58e2c72..10769ae 100644
--- a/playbooks/roles/configure-targethosts/tasks/configure-network-Debian.yml
+++ b/playbooks/roles/configure-targethosts/tasks/configure-network-Debian.yml
@@ -71,7 +71,7 @@
 - name: Ensure systemd resolved.conf has the correct content
   lineinfile:
     path: /etc/systemd/resolved.conf
-    regexp: "^#?DNS=.*$"
+    regexp: '^#?(DNS|dns)\s*=.*$'
     line: "DNS={{ idf.net_config[engine.public_network | default('public')].dns | join(' ') }}"
   when: idf.net_config[engine.public_network | default('public')].dns is defined