public static void sleep(long millis) {
    try {
      Thread.sleep(millis);
    } catch (InterruptedException e) {
      LOG.warn("sleep interrupted", e);
      Thread.currentThread().interrupt();
    }
  }
If interrupted, just prints out the interrupt on STDOUT, resets interrupt and returns
@param millis How long to sleep for in milliseconds.
hbase-common/src/main/java/org/apache/hadoop/hbase/util/Threads.java