public Response listColumns(String user, String db, String table)
    throws HcatException, NotAuthorizedException, BusyException,
    ExecuteException, IOException {
    try {
      return descTable(user, db, table, false);
    } catch (HcatException e) {
      throw new HcatException("unable to show columns for table: " + table,
        e.execBean, e.statement);
    }
  }
Return a json description of the columns.  Same as
describeTable.
hcatalog/webhcat/svr/src/main/java/org/apache/hive/hcatalog/templeton/HcatDelegator.java