Refactor test executors

[G1gg1L3s]

As @Lagovas said here, there is a common pattern of creating an executors with custom arguments. This PR factors this out into a mixin class with already established

Decided to do it as a separate PR, to make PRs atomic in terms of changes and to make review easier.

Checklist

• [x] Change is covered by automated tests
• [x] The coding guidelines are followed
• [x] ~Public API has proper documentation in the Acra documentation site or has PR on documentation repository with new changes~
• [x] ~CHANGELOG.md is updated (in case of notable or breaking changes)~
• [ ] CHANGELOG_DEV.md is updated (Do I have to update it?)
• [x] ~Benchmark results are attached (if applicable)~
• [x] ~Example projects and code samples are up-to-date (in case of API changes)~