Use AllocationStats instead of map

Author: nicktindall

server/src/main/java/org/elasticsearch/cluster/routing/allocation/allocator/DesiredBalanceMetrics.java

@@ -256,8 +256,8 @@ public long undesiredAllocations() {
         return lastReconciliationAllocationStats.undesiredAllocationsExcludingShuttingDownNodes();
     }
 
-    public Map<ShardRouting.Role, RoleAllocationStats> allocationStatsByRole() {
-        return lastReconciliationAllocationStats.allocationStatsByRole();
+    public AllocationStats allocationStatsByRole() {
+        return lastReconciliationAllocationStats;
     }
 
     private List<LongWithAttributes> getUnassignedShardsMetrics() {

server/src/main/java/org/elasticsearch/cluster/routing/allocation/allocator/DesiredBalanceShardsAllocator.java

@@ -438,7 +438,7 @@ public DesiredBalanceStats getStats() {
         );
     }
 
-    public Map<ShardRouting.Role, DesiredBalanceMetrics.RoleAllocationStats> getAllocationStatsByRole() {
+    public DesiredBalanceMetrics.AllocationStats getAllocationStatsByRole() {
         return desiredBalanceMetrics.allocationStatsByRole();
     }