PLAT-433 put the thumbnail under the original dir in the thumb path

Put the thumbnail under the original directory on CEPH. This will ensure that if MW moves the directory under the thumb path, that the existing thumbnails will move with it.

For example, the thumbnails are currently being placed under `//bucket/images/thumb/0/0c/*` when they should be placed under `//bucket/images/thumb/0/0c/original.ext/*`.

https://wikia-inc.atlassian.net/browse/PLATFORM-433

/cc @nmonterroso