run changegroup names are based on the run path but it will contain slashes and
could be very long. So calculate the sha256 sum of the path and use it as the
changegroup name.
* 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