toolTests: Fix undefined name usage introduced by 32713.

pyflakes complained:
./tests/toolTests.py:309: undefined name 'Libvirt'.

Change-Id: Ibb8fb3a8413d97d3ad6dca6ccbb81748facafe84
Signed-off-by: Mooli Tayer <mtayer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/33531
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>