Improve testing connection closes for parallel test run

[Lagovas]

Improved test case to use configured db name for MySQL instead of default and rely only on connections of configure database instead of whole database. It helps to run tests parallely.

Checklist

• [ ] Change is covered by automated tests
• [ ] The coding guidelines are followed
• [ ] Public API has proper documentation in the Acra documentation site or has PR on documentation repository with new changes
• [ ] CHANGELOG.md is updated (in case of notable or breaking changes)
• [ ] CHANGELOG_DEV.md is updated
• [ ] Benchmark results are attached (if applicable)
• are up-to-date (in case of API changes)