app/testpmd: use hotplug failure handler

app/testpmd: use hotplug failure handler

This patch use testpmd for example, to show how an app smoothly handle
failure when device be hot-unplug. Except that app should enabled the
device event monitor and register the hotplug event’s callback, it also
need enable hotplug handle mechanism before running. Once app detect the
removal event, the hot-unplug callback would be called. It will first stop
the packet forwarding, then stop the port, close the port, and finally
detach the port to clean the device and release the resources.

Signed-off-by: Jeff Guo <jia.guo@intel.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Bernard Iremonger <bernard.iremonger@intel.com>