Prevent cloud-init from overwriting /etc/hosts (#707)

* Prevent cloud-init from overwriting /etc/hosts

Some cloud vendors attempt to overwrite /etc/hosts, which is managed by set-fqdn
and other NS8 actions. This commit prevents cloud-init from overwriting its
contents and losing NS8 settings.

* Disable the hostname update

The host name is controlled by action set-fqdn. Once NS8 is installed
only NS8 can manage it. Changing the hostname by other ways can lead to
inconsistent cluster setup.

Refs NethServer/dev#6993

core/imageroot/var/lib/nethserver/node/install-finalize.sh

@@ -19,6 +19,11 @@ if ! grep -q ' cluster-leader$' /etc/hosts; then
     echo "127.0.0.1 cluster-localnode" >> /etc/hosts
 fi
 
+if [ -f /etc/cloud/cloud.cfg ]; then
+    echo "Remove update_etc_hosts cloud-init module:"
+    sed -i.orig -r '/-\s*update_etc_hosts/ d ; /-\s*update_hostname/ d' /etc/cloud/cloud.cfg || :
+fi
+
 echo "Generate WireGuard VPN key pair:"
 (umask 0077; wg genkey | tee /etc/nethserver/wg0.key | wg pubkey) | tee /etc/nethserver/wg0.pub