(aio) Default thread pool should be configured so that threads terminated after a timeout period

In the asycnhronous I/O API then the default thread pool is a cached thread pool as it may be shared by different applications/components in the same VM. These therads remain running and do not terminate after an idle time. We should change so that they terminate after 60s or so when not used. The only exception is older editions of Windows as they do not support thread agnostic I/O. This means that on older versions of Windows then the threads cannot terminate.