Handle InstanceNotFound in libvirt list_instances.
Handle InstanceNotFound in libvirt list_instances.

Updates the libvirt driver so that InstanceNotFound is
handled within the list_instances function. This
can occur if an instance is deleted while the
list_instances function is processing.

Fixes LP Bug #1032741.
Change-Id: I97c9533f8b37957e71237c610ac360fbf9f57b9a

n0ano/ganttclient