Run migration with NotFound exception as well
Run migration with NotFound exception as well

Gnocchi start returning regular 404 when requesting resource that do not
exist [1]. That means, that in case of 404, which is also excpected,
we just fail resource creation.

[1] http://paste.openstack.org/show/796938/

Change-Id: Ie5f8caba3111db7e7e8e50b9bc58c6e8de606338

openstack/ceilometer,openstack/ceilometer