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.
forkCount is not available in the surefire version that we use (still some old 2.12.1 or so...). Perhaps we should update to 2.16 or 2.17... ;)
But forkMode=once / forkCount=1 is the default anyway (back then and still today)...