Implement Column default constraint

[wangyum]

DEFAULT clause is a domain constraint which lets user specify a value for domain i.e. column to be used in absence of user specified value i.e. in absence of column reference.
It is an ANSI SQL, Feature ID: E141-07.

CREATE TABLE [ IF NOT EXISTS ]
table_name (
  { column_name data_type [DEFAULT <default option>] [ COMMENT comment ] [ WITH ( property_name = expression [, ...] ) ]
  | LIKE existing_table_name [ { INCLUDING | EXCLUDING } PROPERTIES ] }
  [, ...]
)
[ COMMENT table_comment ]
[ WITH ( property_name = expression [, ...] ) ]

https://issues.apache.org/jira/browse/HIVE-18726