`lts` was choosen to reflect a "long term storage" but currently it's just an
object storage implementation. So use this term and "ost" as its abbreviation
(to not clash with "os").
* Remove all the small index files on the lts
* Keep on s3 only a full index of all runs containing the runid, grouppath and phase
million of runs can take only some hundred of megabytes
* Periodically create a new dump of the index
