`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").
* client: always parse the json error message field and return its contents
* Use ErrBadRequest and ErrNotFound in every handler and command
* Gateway: by default pass underlying service error (configstore, runservice) to
client keeping the status code and message. In future, if some errors must be
masked, we should change the specific parts that need special handling.
Simone Gotti