Fix invalid uuid warnings in object unit tests

Fix invalid uuid warnings in object unit tests

Currently 'tox -epy27 -- --regex cinder.tests.unit.objects' emits
74 FutureWarnings from oslo.versionedobjects about invalid uuids
as documented here[1].

This commit changes these tests to use valid uuids so that when
they are run these warnings are no longer emitted.

[1] http://docs.openstack.org/developer/oslo.versionedobjects/api/fields.html#oslo_versionedobjects.fields.UUIDField
Change-Id: I8c8ac25f695adec61b5e506ddf99780448ee224e