Handle the task dependencies conditions:
* on_success (default if no conditions are specified)
* on_failure
* on_skipped
Not the runservice won't stop run but continue executing tasks that depends on a
parent also if this is failed
* 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.
