dblog_settings tests prove nothing

Problem/Motivation

#2590993: Create stub entities with proper default values got an exception in d7/MigrateDblogConfigsTest, the tl;dr of which is that it exposed the fact that the dblog_row_limit variable it's supposed to be migrating is not set in the test fixture. The assertions pass (without the stub patch) because the value they're testing for, 1000, is the default value in D8. The d6 test has the same issue - the value in the fixture is 1000, so we're proving nothing by asserting the final value as 1000.

Proposed resolution

Set the dblog_row_limit variable in both the D6 and D7 test fixtures to something other than 1000, and assert that value in the tests.

Remaining tasks

Fix it

User interface changes

N/A

API changes

None

Data model changes

None