[Improvement] Dependent tasks support dependent policies

dolphinscheduler-master/src/main/java/org/apache/dolphinscheduler/server/master/runner/task/TaskProcessorFactory.java

@@ -47,7 +47,8 @@ public final class TaskProcessorFactory {
     static {
         for (ITaskProcessor iTaskProcessor : ServiceLoader.load(ITaskProcessor.class)) {
             try {
-                PROCESS_MAP.put(iTaskProcessor.getType(), (Constructor<ITaskProcessor>) iTaskProcessor.getClass().getConstructor());
+              if (PROCESS_MAP.get(iTaskProcessor.getType()) == null )
+                  PROCESS_MAP.put(iTaskProcessor.getType(), (Constructor<ITaskProcessor>) iTaskProcessor.getClass().getConstructor());
             } catch (NoSuchMethodException e) {
                 throw new IllegalArgumentException("The task processor should has a no args constructor", e);
             }