set AntClassLoader property as in pom

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@20575 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/build-script/Cobertura.groovy

@@ -55,6 +55,7 @@ public class Cobertura {
                 formatter(type:"xml")
             }
             sysproperty(key:"net.sourceforge.cobertura.datafile",value:ser)
+	    sysproperty(key:"hudson.ClassicPluginStrategy.useAntClassLoader",value:"true")
         }
     }