AutoYaST: another write_hostname regression (bnc#796580)

If keep_install_network=true and dns/write_hostname is unspecified,
use the product default (which is false on SLES), thus not writing
127.0.0.2 to /etc/hosts.

(fixing a regression introduced in 2.17.166)

src/clients/lan_auto.ycp

@@ -301,11 +301,21 @@ else if(func == "Import") {
         // copy the keys/values that are not existing in the XML
         // so we merge the inst-sys settings with the XML while XML
         // has higher priority
+        //
+        // bnc#796580 The problem with this is that due to compatibility with
+        // older profiles, a missing element may have a different meaning than
+        // "use what the filesystem/kernel currently uses".
+        // In particular, a missing write_hostname [1] means
+        // "use the product default from DVD1/control.xml".
+        // Other elements may have similar problems,
+        // to be fixed post-PTF for maintenance.
         if (! haskey(param, "dns")) {
             param["dns"] = $[];
         }
         foreach( string key, any value, dns, {
-            if( ! haskey( param["dns"]:$[], key ) ) {
+
+            if( ! haskey( param["dns"]:$[], key )
+                && key != "write_hostname" ) { // [1] ^
                 y2milestone("(dns) taking %1 from inst-sys. Value = %2", key, value);
                 param["dns",key] = value;
             }