@Override
      protected void chore() {
        try {
          user.checkTGTAndReloginFromKeytab();
        } catch (IOException e) {
          LOG.error("Got exception while trying to refresh credentials: " + e.getMessage(), e);
        }
      }
Checks if security is enabled and if so, launches chore for refreshing kerberos ticket.
@return a ScheduledChore for renewals.
hbase-common/src/main/java/org/apache/hadoop/hbase/AuthUtil.java