Fix server test RemoveFromParentLockingTest

Change-Id: Ib3af43a1b6945db00194775fbb2a91b4b495ee9b

server/src/test/java/com/vaadin/tests/server/component/abstractsinglecomponentcontainer/RemoveFromParentLockingTest.java

 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
 
+import org.junit.After;
 import org.junit.Assert;
+import org.junit.Before;
 import org.junit.Test;
 
 import com.vaadin.server.VaadinRequest;
 
 public class RemoveFromParentLockingTest {
 
+    @Before
+    @After
+    public void cleanCurrentSession()
+    {
+        VaadinSession.setCurrent(null);
+    }
+
     private static VerticalLayout createTestComponent() {
         VaadinSession session = new VaadinSession(null) {
             private final ReentrantLock lock = new ReentrantLock();
                     "Cannot remove from parent when the session is not locked."
                             + " Furthermore, there is another locked session, indicating that the component might be about to be moved from one session to another.",
                     e.getMessage());
-        } finally {
-            VaadinSession.setCurrent(null);
         }
     }
 
             notLockedComponent.addComponent(lockedComponent);
         } catch (AssertionError e) {
             // All is fine, don't care about the exact wording in this case
-        } finally {
-            VaadinSession.setCurrent(null);
         }
     }