Extended PHPUnit_Extensions_Database_TestCase for new KernelDbTestCase c...

| Q             | A
| ------------- | ---
| Bug fix?      | [no]
| New feature?  | [yes]
| BC breaks?    | [no]
| Deprecations? | [no]
| Tests pass?   | [yes]
| Fixed tickets | 
| License       | MIT
| Doc PR        | 

For those that want to unit test with PHPUnit_Extensions_Database_TestCase.