I agree with Ivan: puppet should not convert any existed resource to a new format. From my POV, the most appropriate solution is to fix nailgun (update astute.yaml if ceph is enabled with addition RAW image info) and add RAW image to cirros-testvm package or add new cirros-testvm-raw package.
Otherwise, puppet-convert solution looks like hardcode.
I agree with Ivan: puppet should not convert any existed resource to a new format. From my POV, the most appropriate solution is to fix nailgun (update astute.yaml if ceph is enabled with addition RAW image info) and add RAW image to cirros-testvm package or add new cirros-testvm-raw package.
Otherwise, puppet-convert solution looks like hardcode.