CA-153556: Perform sanity check and lowercase for hotfix UUIDs

Signed-off-by: Sharad Yadav <sharad.yadav@citrix.com>
This could be shortened. You could just have
```ocaml
let uuid = String.lowercase uuid in
if not Uuid.is_uuid uuid
then raise (Invalid_patch_uuid uuid);
uuid
```

It's a very small thing but it seems slightly clearer to me since the return value is at the end.