Support ALTER TABLE for JDBC tables

Currently ALTER TABLE is not supported for data source tables since connection credentials are set as in single initString. See https://github.com/apache/impala/blob/master/fe/src/main/java/org/apache/impala/analysis/AlterTableStmt.java#L103-L108.
IMPALA-12793 change the syntax for creating JDBC table. The configuration of connection credentials - url, username, password, jdbc driver, etc, are set as table properties. We should allow user to change these properties or edit a column name via ALTER TABLE statement.