Use only singe thread for POJA applications

[andriy-dmytruk]

Feature description

Use only single (main) thread for POJA applications. It seems this could be achieved with -XX:ActiveProcessorCount=1. Not sure about other ways.

[graemerocher]

not sure how this can be achieved here?

[andriy-dmytruk]

There is also the java.util.concurrent.ForkJoinPool.common.maximumSpares system property. If we can set it before ForkJoinPool class is loaded, then that would work.

If it cannot be achieved, then I will add it to documentation.