public Retry<E> sleep(long duration, TimeUnit unit) {
    Preconditions.checkArgument(duration >= 0);
    this.sleepMilliseconds = unit.convert(duration, TimeUnit.MILLISECONDS);
    return this;
  }
Set the sleep time between retries.

@param duration the time to sleep
@param unit the unit of time of duration
@return the instance for further configuration
jib-core/src/main/java/com/google/cloud/tools/jib/cache/Retry.java