rename the previous posix storage to posixflat and make it currently not user
selectable (since I'm not sure it's really worth using it).
The new posix storage uses the filesystem without any escaping so it's not a
real flat namespace.
This isn't a real issue since also minio is not a flat namespace and we are so
forced to use it like a hierarchycal filesystem.
Logs and archives can be shared by multiple runs. So removing a run doesn't
imply that we could also remote the logs and archives since they could be
"referenced" by another run.
Store also the runids as specific objects along with the logs and archives so,
we'll remove them only when no runids objects exist.
Also if they are logically part of the runservice the names runserviceExecutor
and runserviceScheduler are long and quite confusing for an external user
Simplify them separating both the code parts and updating the names:
runserviceScheduler -> runservice
runserviceExecutor -> executor
