[FIXED JENKINS-8892] set the classloader for GroovyShell

Otherwise plugin classes won't resolve.

changelog.html

@@ -64,6 +64,9 @@ Upcoming changes</a>
   <li class=bug>
     Post build action deploy to maven repository can fail when using "use private maven repository option"
     (<a href="http://issues.jenkins-ci.org/browse/JENKINS-8711">issue 8711</a>)    
+  <li class=bug>
+    Groovy CLI command was failing to resolve plugin classes
+    (<a href="http://issues.jenkins-ci.org/browse/JENKINS-8892">issue 8892</a>)    
   <li class=rfe>
     Exposing more key variables to the Groovy CLI command.
 </ul>

core/src/main/java/hudson/cli/GroovyCommand.java

@@ -89,7 +89,7 @@ public class GroovyCommand extends CLICommand implements Serializable {
             }
         }
 
-        GroovyShell groovy = new GroovyShell(binding);
+        GroovyShell groovy = new GroovyShell(Hudson.getInstance().getPluginManager().uberClassLoader, binding);
         groovy.run(loadScript(),"RemoteClass",remaining.toArray(new String[remaining.size()]));
         return 0;
     }