Comment 1 for bug 974293

Seems that the issue occurs due to the tearDown( ) method in test_libvirt:LibvirtConnectionTestCase.

https://github.com/openstack/nova/blob/master/nova/tests/test_libvirt.py#L2314

Here is the tearDown code snippet:

    def tearDown(self):
        super(LibvirtConnectionTestCase, self).tearDown()

        try:
            shutil.rmtree(flags.FLAGS.instances_path)
        except Exception:
            pass