[JENKINS-20772] Only show error message in dialog

This change removes the superfluous UI elements around the error
message if possible. Otherwise, fall back to existing behavior
of adding entire page to iframe.

core/src/main/resources/jenkins/model/Jenkins/oops.jelly

@@ -41,6 +41,7 @@ THE SOFTWARE.
       <h1 style="text-align: center">
         <img src="${imagesURL}/rage.png" height="179" width="154"/> <span style="font-size:50px"><st:nbsp/>${%Oops!}</span>
       </h1>
+      <div id="error-description">
       <p>
         ${%problemHappened}
         ${%checkJIRA}
@@ -51,6 +52,7 @@ THE SOFTWARE.
       </p>
       <h2>${%Stack trace}</h2>
       <pre style="margin:2em; clear:both">${h.printThrowable(request.getAttribute('javax.servlet.error.exception'))}</pre>
+      </div>
     </l:main-panel>
   </l:layout>
 </j:jelly>
\ No newline at end of file

core/src/main/resources/lib/form/apply/apply.js

@@ -12,7 +12,7 @@ Behaviour.specify("INPUT.apply-button", 'apply', 0, function (e) {
         });
 
         responseDialog.setHeader("Error");
-        responseDialog.setBody("<div id='"+containerId+"'></iframe>");
+        responseDialog.setBody("<div id='"+containerId+"'></div>");
         responseDialog.render(document.body);
         var target; // iframe
 
@@ -42,7 +42,12 @@ Behaviour.specify("INPUT.apply-button", 'apply', 0, function (e) {
                 } else {
                     // otherwise this is possibly an error from the server, so we need to render the whole content.
                     var doc = target.contentDocument || target.contentWindow.document;
-                    $(containerId).appendChild(doc.getElementsByTagName('body')[0]);
+                    var error = doc.getElementById('error-description');
+                    if (!error) {
+                        // fallback if it's not a regular error dialog from oops.jelly: use the entire body
+                        error = doc.getElementsByTagName('body')[0];
+                    }
+                    $(containerId).appendChild(error);
                     var r = YAHOO.util.Dom.getClientRegion();
                     responseDialog.cfg.setProperty("width",r.width*3/4+"px");
                     responseDialog.cfg.setProperty("height",r.height*3/4+"px");