YARN-8894. Improve InMemoryPlan#toString. Contributed by BELUGA BEHR.

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/reservation/InMemoryPlan.java

@@ -866,9 +866,9 @@ public class InMemoryPlan implements Plan {
   public String toString() {
     readLock.lock();
     try {
-      StringBuffer planStr = new StringBuffer("In-memory Plan: ");
+      StringBuilder planStr = new StringBuilder("In-memory Plan: ");
       planStr.append("Parent Queue: ").append(queueName)
-          .append("Total Capacity: ").append(totalCapacity).append("Step: ")
+          .append(" Total Capacity: ").append(totalCapacity).append(" Step: ")
           .append(step);
       for (ReservationAllocation reservation : getAllReservations()) {
         planStr.append(reservation);