dd::Raw_record::store() asserts in debug version due to error in
conversion of timestamp data.

The sequence leading to assert is :
- dd::Object is cached with local time stored for timestamp columns.
- time_zone value is changed. Cached dd::Object is not aware of the change.
- Any DDL operation which calls Dictionary_client::update() copies data
  from existing dd::Object.
- During this copy, the timestamp column data is treated as local time
  and converted to epoch time according to value of time_zone before
  storing.

 - If timestamp value becomes invalid (negative) during conversion,
   it leads to an assert.
 - For invalid value of timestamp, release build will give an error
   for the DDL commands.
 - For valid value of timestamp, the value of create_time will change
   with DDL.

Fix:

- Store timestamp data for dd::Objects in GMT time_zone.
- Cache timestamp data for dd::Objects in GMT time_zone.
- Implement function gmt_time_to_local_time to convert GMT time
  to local time.
- Return timestamp data based on the request flag by caller function.
  - Within dictionary framework, timestamp data should be requested
    with flag as false to get GMT time_zone data.
  - Server should request timestamp column data with flag as true
    to get local time_zone data.