Catch more accuracy exception for _lookup_by_name

When an instance is not found by libvirtd, _lookup_by_name in libvirt
driver raises InstanceNotFound. This patch catchs this exception instead
of NotFound who is the father of InstanceNotFound.

Closes-Bug: #1222663
Change-Id: I1b4ce8f6c44eef29617a42151152cda2159a0088
Merge "Catch more accuracy exception for _lookup_by_name"