[ONOS-5797] GroupService: add setBucketsForGroup

Add method to set all buckets from a group, overwriting the
previous group buckets entirely. Useful for edits that before
required two operations: removing the buckets and then adding
others. It can all be done with one OF message in the end.

Change-Id: Ic5669603ed4fd18b8efaa8d0253ab9d7b1e870f5
diff --git a/core/store/dist/src/main/java/org/onosproject/store/group/impl/DistributedGroupStore.java b/core/store/dist/src/main/java/org/onosproject/store/group/impl/DistributedGroupStore.java
index 28e3302..88a1d54 100644
--- a/core/store/dist/src/main/java/org/onosproject/store/group/impl/DistributedGroupStore.java
+++ b/core/store/dist/src/main/java/org/onosproject/store/group/impl/DistributedGroupStore.java
@@ -719,6 +719,10 @@
     private List<GroupBucket> getUpdatedBucketList(Group oldGroup,
                                                    UpdateType type,
                                                    GroupBuckets buckets) {
+        if (type == UpdateType.SET) {
+            return buckets.buckets();
+        }
+
         List<GroupBucket> oldBuckets = oldGroup.buckets().buckets();
         List<GroupBucket> updatedBucketList = new ArrayList<>();
         boolean groupDescUpdated = false;