Implement wait for termianation

src/de/steamwar/bungeecore/Subserver.java

@@ -130,6 +130,16 @@ public class Subserver implements Runnable {
         }
     }
 
+    public void waitForTermination(){
+        try {
+            if(!process.waitFor(5, TimeUnit.MINUTES))
+                process.destroy();
+        }catch(InterruptedException e){
+            logger.log(Level.SEVERE, "Subserver stop interrupted!", e);
+            Thread.currentThread().interrupt();
+        }
+    }
+
     static void shutdown(){
         while (!serverList.isEmpty()) {
             Subserver server = serverList.get(0);