static void setRootLevel(String levelName) {
    String loggerName = org.apache.logging.log4j.LogManager.getRootLogger().getName();
    setLogLevel(loggerName, levelName);
  }
The actual class for operating on log4j2.
<p/>
This class will depend on log4j directly, so callers should not use this class directly to avoid
introducing log4j2 dependencies to downstream users. Please call the methods in
{@link Log4jUtils}, as they will call the methods here through reflection.
hbase-logging/src/main/java/org/apache/hadoop/hbase/logging/InternalLog4jUtils.java