Remove devices gracefully when shutting down VMM

[justxuewei]

The types of devices that should implement gracefully shutting down include:

• virtio-block (implemented)
• virtio-net (implemented in dbs-virtio-devices: Clear resources when removing virtio-net and vsock devices #277)
• virtio-vsock (implemented in dbs-virtio-devices: Clear resources when removing virtio-net and vsock devices #277)
• vhost-net
• virtio-mem

[justxuewei]

#277 implements graceful removal for virtio-net and virtio-vsock devices.

[justxuewei]

@studychao Could you reopen this issue? Because the vhost-net and the virtio-mem haven't implemented this yet.

[studychao]

@studychao Could you reopen this issue? Because the vhost-net and the virtio-mem haven't implemented this yet.

Done, thanks. Seem like Github will automatically close the issue if related PR is merged..

[studychao]

kata-containers/kata-containers#6684
will be used to track this issue