YARN-10545. Improve the readability of diagnostics log in yarn-ui2 web page. apache#2540

Contributed by kyoty.

Author: echohlne

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-ui/src/main/webapp/app/templates/yarn-app/info.hbs

@@ -42,7 +42,7 @@
         <div class="panel-heading">
           Diagnostics
         </div>
-        <div class="panel-body">{{model.app.diagnostics}}</div>
+        <div class="panel-body" style="white-space: pre-wrap;">{{model.app.diagnostics}}</div>
       </div>
     {{else}}
       <div class="panel panel-default">