add qmeventd

add qmeventd

this adds a program that can listen to qemu qmp events on a given socket
and if a shutdown event followed by a disconnected socket occurs,
executes qm cleanup with arguments that indicate if the
vm was closed gracefully and whether the guest initiated it

this is useful if we want to cleanup after the qemu process exited,
e.g. tap devices, vgpus, etc.

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>