Support Oracle CLOB type in beeline

We can use beeline as a JDBC client to access RDBMS such as Oracle. Sometimes Oracle JDBC driver will return a CLOB object instead of a String object if the string is too long. Beeline used to work well with CLOB type but it's broken by HIVE-14786:

https://github.com/apache/hive/blob/2a760dd607e206d7f1061c01075767ecfff40d0c/beeline/src/java/org/apache/hive/beeline/Rows.java#L169

In the above line, when Oracle JDBC driver returns a CLOB object, it returns a string like "oracle.sql.CLOB@2f7c7260". In this case, we should use ResultSet.getString() rather than ResultSet.getObject().toString().