CPU usage was calculated without taking SMP VM into account.

When we update a VM configuration while it is running, for example a change in
the network interfaces, we recreate a domain from the running XML which is fine
but this is not valid anymore when the VM is stopped.
So in the latter case, we keep an attribute on the VM indicating if we need to
recreate the VM instance from the XML when it stops.

Since a network interface cannot change.

Define a decorator for libvirt handlers, those can be used only when the
connection to the libvirt is active

The tag was not removed from TagDB when the libvirt connection was lost.

Only one network interface was shown in the tags.

With the permission of Romain Degez, CTO of Smartjog.

Signed-off-by: Sébastien Luttringer <sebastien.luttringer@smartjog.com>

Libvirtd version 0.8.8 is capable of handling connections to virtio consoles but
the Python API is broken.

Tunnel endpoints are now automaticaly closed by default.