Fix tests for migration 227 to check sqlite

The _check_227 test skips for sqlite despite modifying that dialect.
It also has a redundant check for an existing row that doesn't work
when snake-walking the migration tests.

Change-Id: I58d9a539868d50e345a6dfa78918e04a4a699a68
Closes-Bug: 1240751
Merge "Fix tests for migration 227 to check sqlite"