Fix SelectAllRowsTest to not alter existing DesiredCapabilities

Change-Id: I5fe09c76f681ae25a9bb9f78e0eaca4ce4c57951

uitest/src/com/vaadin/tests/components/table/SelectAllRowsTest.java

@@ -39,7 +39,8 @@ public class SelectAllRowsTest extends MultiBrowserTest {
 
     @Override
     protected DesiredCapabilities getDesiredCapabilities() {
-        DesiredCapabilities cap = super.getDesiredCapabilities();
+        DesiredCapabilities cap = new DesiredCapabilities(
+                super.getDesiredCapabilities());
         cap.setCapability("requireWindowFocus", true);
         return cap;
     }