With remote storage, swap disk size changed after resize-revert

There seems to be an issue (discovered in Pike) where ceph-backed swap does not return to the original size if a resize operation is reverted.

Steps to reproduce:
1) Configure compute nodes to use remote ceph-backed storage for instances.
2) Launch a vm with with ephemeral and swap disk. (The swap disk will be RBD-backed.)
3) Resize vm to a new flavor with larger swap disk size. The swap disk will be resized to the larger size.
4) Resize-revert to original flavor.
5) Check actual disk sizes from within the VM and from ceph directly.

Expected behaviour:
VM swap disk size should be reverted back to original size.

Actual behaviour:
VM swap disk remains at the larger size.