YARN-6764. Simplify the logic in FairScheduler#attemptScheduling. Contributed by Yufei Gu.

(cherry picked from commit 3de47ab5ea5cb75805a03010dc72e11b0cf6c173)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/FairScheduler.java

@@ -1050,16 +1050,13 @@ public class FairScheduler extends
         Resource maxResourcesToAssign = Resources.multiply(
             node.getUnallocatedResource(), 0.5f);
         while (node.getReservedContainer() == null) {
-          boolean assignedContainer = false;
           Resource assignment = queueMgr.getRootQueue().assignContainer(node);
-          if (!assignment.equals(Resources.none())) {
-            assignedContainers++;
-            assignedContainer = true;
-            Resources.addTo(assignedResource, assignment);
-          }
-          if (!assignedContainer) {
+          if (assignment.equals(Resources.none())) {
             break;
           }
+
+          assignedContainers++;
+          Resources.addTo(assignedResource, assignment);
           if (!shouldContinueAssigning(assignedContainers, maxResourcesToAssign,
               assignedResource)) {
             break;