CSTACK-18_1: corrected junit as per latest changes

Author: rajiv-jain-netapp

plugins/storage/volume/ontap/src/test/java/org/apache/cloudstack/storage/service/StorageStrategyTest.java

@@ -146,6 +146,11 @@ public CloudStackVolume getCloudStackVolume(
             return null;
         }
 
+        @Override
+        public CloudStackVolume snapshotCloudStackVolume(CloudStackVolume cloudstackVolume) {
+            return null;
+        }
+
         @Override
         public AccessGroup createAccessGroup(
                 org.apache.cloudstack.storage.service.model.AccessGroup accessGroup) {