[buteo-sync-plugin-caldav] Update href and etag as soon as a PUT request is finished with success. Contributes to MER#2040
Update href and etag as soon as a PUT request is finished with success. This simplifies the retrieval of missing etags and update of them. Since a finished PUT request with success means the data are on the server, there is sense to update the href and etag values immediately and not after all PUT requests have succeeded. This avoid some assumptions on next sync cycle on broken incidence with respect to sync status.
This MR also corrects a minor bug: when one deletes a persistent exception on device, the whole series is PUT on server, which is fine, but new etag is not propagated on device since, etags were propagated only for localModifications and localAdditions lists.