[master] Port transport graceful shutdown feature from 2.3.
[master] 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.
(cherry picked from commit 4abde5c210713c2f24656e301d8b957d037daa86)
[master] Port changes for https://java.net/jira/browse/GRIZZLY-1558 (Leverage Transport graceful shutdown feature in HttpServer/NetworkListener) to master.
[master] + fix issue #1572
https://java.net/jira/browse/GRIZZLY-1572

"NIOTransportTest fails: "java.net.BindException: Address already in use""
(cherry picked from commit fa4768f09360cf6eaa376030986dc7fd83339f4c)
[master] [2.3.x] + rework: fix issue #1572
https://java.net/jira/browse/GRIZZLY-1572

"NIOTransportTest fails: "java.net.BindException: Address already in use""
(cherry picked from commit 0318811a375f33ea953fb9c3425caaca07572911)
[master] Port findbugs changes from 2.3 to master.
[master] Port connection-pool and associated samples from 2.3 to master.