[FEATURE] Checkstyle violations fail the Build

src/test/java/net/sourceforge/plantuml/servlet/ServerUtils.java

@@ -8,7 +8,7 @@ import org.eclipse.jetty.webapp.WebAppContext;
 
 public class ServerUtils {
 
-    Server server;
+    private Server server;
 
     public ServerUtils(boolean start) throws Exception {
         server = new Server(new InetSocketAddress("127.0.0.1", 0));

src/test/java/net/sourceforge/plantuml/servlet/TestUtils.java

@@ -20,4 +20,8 @@ public class TestUtils {
      */
     public static final String SEQBOB = "SyfFKj2rKt3CoKnELR1Io4ZDoSa70000";
 
+    protected TestUtils() {
+        // prevents calls from subclass
+        throw new UnsupportedOperationException();
+    }
 }