rdbms: clean up non-native Database::replace() code

rdbms: clean up non-native Database::replace() code

* Make sure all unique keys specified have all their values
  provided to avoid large bogus DELETEs. Do not ignore them
  in such cases either, as that would cause inconsistencies
  between the native and non-native case. Use an exception.
* Make ChangeTags caller clearer that the list of indexes
  is not a list of fields for a single index. Also, avoid
  mentioning indexes for values not defined in the new
  records, as this causes errors or inconsistencies with
  the native vs non-native case.
* This also fixes the "Undefined index: ts_log_id" error
  when running unit tests on postgres.

Change-Id: I30263df22066bd6d4836202b1bcad5d1aa1e7383