public static boolean enabled(TableDescriptor desc, Class<? extends Constraint> clazz)
    throws IOException {
    // get the kv
    Pair<String, String> entry = getKeyValueForClass(desc, clazz);
    // its not enabled so just return false. In fact, its not even present!
    if (entry == null) {
      return false;
    }

    // get the info about the constraint
    Configuration conf = readConfiguration(entry.getSecond());

    return conf.getBoolean(ENABLED_KEY, false);
  }
Check to see if the given constraint is enabled.
@param desc  {@link TableDescriptor} to check.
@param clazz {@link Constraint} to check for
@return <tt>true</tt> if the {@link Constraint} is present and enabled. <tt>false</tt>
        otherwise.
@throws IOException If the constraint has improperly stored in the table
hbase-server/src/main/java/org/apache/hadoop/hbase/constraint/Constraints.java