public static Kryo borrowKryo() {
    return borrowKryo(null);
  }
By default, kryo pool uses ConcurrentLinkedQueue which is unbounded. To facilitate reuse of
kryo object call releaseKryo() after done using the kryo instance. The class loader for the
kryo instance will be set to current thread's context class loader.

@return kryo instance
ql/src/java/org/apache/hadoop/hive/ql/exec/SerializationUtilities.java