Exceptional parallel execution on @NotThreadSafe type.

We want to execute tests in parallel.
 In some cases some tests want to be executed in a single Thread instance.
 For instance I am using Embedded Container OpenEJB which is singleton, thus does not support parallelism.
 Other tests want to be executed in parallel anyway.
 This simple principle avoids parallel execution in an elegant way in src/test/java.
It was done like this with `javax.annotation.concurrent.NotThreadSafe` but the problem with this annotation is that it is not available in runtime.