Option to make test tasks run in isolation

[jjohannes]

If you use the configuration cache, Gradle runs more tasks in parallel as before. In testing however, you may need certain test tasks to run in isolation from other test tasks (because they require exclusive access to most of the machine resources). This can be solved by using a build service with maxParallelUsages = 1.

This plugin could offer an option to configure this for a test suite.