[2.3.x] Incremental changes for https://java.net/jira/browse/GRIZZLY-1546.
 - Introduce new callback that will be invoked when the transport is being shutdown forcefully
    after a graceful shutdown request.
[2.3.x] + implement task #1551
https://java.net/jira/browse/GRIZZLY-1551
"Create connection-pool sample"