core: update grizzly thread pool sizes to best-practice configuration

Give threads more "natural" names.
thread pool configuration based on Glassfish developers recommendations:

   worker thread pool size: #CPUs*2, min 5
   selector threads pool size: #CPUs, if no worker threads configured,
                               #CPUs/4, if worker threads configured,  min 2

Following changes will make arbitrary numbers possible.

Acked-by: Albert Rossi
Target: master