HDDS-501. AllocateBlockResponse.keyLocation must be an optional field. Contributed by Arpit Agarwal.

hadoop-ozone/common/src/main/proto/OzoneManagerProtocol.proto

@@ -324,7 +324,7 @@ message AllocateBlockRequest {
 
 message AllocateBlockResponse {
     required Status status = 1;
-    required KeyLocation keyLocation = 2;
+    optional KeyLocation keyLocation = 2;
 }
 
 message CommitKeyRequest {