public static void grant(Connection connection, final String namespace, final String userName,
    final Permission.Action... actions) throws Throwable {
    grant(connection, namespace, userName, true, actions);
  }
Grants permission on the specified namespace for the specified user. If permissions on the
specified namespace exists, later granted permissions will override previous granted
permissions.
@param connection The Connection instance to use
@param namespace  the namespace
@param userName   the user name
@param actions    the actions
hbase-client/src/main/java/org/apache/hadoop/hbase/security/access/AccessControlClient.java