libvirt: Test disk creation in test_hard_reboot
libvirt: Test disk creation in test_hard_reboot

This test was asserting a call to _create_images_and_backing in a way
that didn't validate the data passed in any way. We update this to
instead validate that the expected disks are created.

This test highlights a bug in _create_images_and_backing, which is
passing a full path in place of a disk name. This will be fixed by
removing the call to _create_images_and_backing in a subsequent
commit.

This also allows us to validate the future removal of the call to
_create_images_and_backing.

Implements: bp/libvirt-imagebackend-refactor
Change-Id: I9d87c8c66f7a9ee15d0c26e8d514cd7b0eea1e09

klmitch/nova,gooddata/openstack-nova,openstack/nova,rahulunair/nova,jianghuaw/nova,gooddata/openstack-nova,vmturbo/nova,mikalstill/nova,Juniper/nova,phenoxim/nova,rajalokan/nova,Juniper/nova,hanlind/nova,vmturbo/nova,Juniper/nova,vmturbo/nova,rahulunair/nova,phenoxim/nova,klmitch/nova,rajalokan/nova,jianghuaw/nova,klmitch/nova,rajalokan/nova,mikalstill/nova,gooddata/openstack-nova,openstack/nova,jianghuaw/nova,klmitch/nova,mahak/nova,jianghuaw/nova,hanlind/nova,mahak/nova,mahak/nova,vmturbo/nova,Juniper/nova,rahulunair/nova,mikalstill/nova,openstack/nova,rajalokan/nova,gooddata/openstack-nova,hanlind/nova