QemuGuestAgent does not work

[Justin Lamp]

Hey,

right now it is impossible to create VMs with the qemu-guest-agent enabled. Starting a VM with it will need access to `/var/lib/libvirt/qemu` in order to create the socket in that directory. As this directory does not exist within the snap, the VM fails to start. Unfortunately nova does not have a way to change this path.

```python
    def _add_qga_device(self, guest, instance):
        qga = vconfig.LibvirtConfigGuestChannel()
        qga.type = "unix"
        qga.target_name = "org.qemu.guest_agent.0"
        qga.source_path = ("/var/lib/libvirt/qemu/%s.%s.sock" %
                          ("org.qemu.guest_agent.0", instance.name))
        guest.add_device(qga)
```

src: nova/virt/libvirt/driver.py

[James Page (james-page)]

This will require either the use of an layout (not sure we can do those into SNAP_DATA) or a patch to allow this directory to be configured via nova.