Check for blank default domain name

src/freedombone

   fi
   # if this is exclusively a cloud setup
   if [[ $SYSTEM_TYPE == "$VARIANT_CLOUD" ]]; then
+      if [ ! $DOMAIN_NAME ]; then
+          echo 'No default domain name when installing cloud variant'
+          exit 5380
+      fi
       OWNCLOUD_DOMAIN_NAME=$DOMAIN_NAME
   fi
   if [ ! $OWNCLOUD_DOMAIN_NAME ]; then