default void preListSnapshot(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final SnapshotDescription snapshot) throws IOException {
  }
Called before listSnapshots request has been processed.
@param ctx      the environment to interact with the framework and master
@param snapshot the SnapshotDescriptor of the snapshot to list
hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/MasterObserver.java