api: propagate Litle errors to the caller

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
api: fix report group string

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
api: handle UUID objects from Kill Bill

Until we have custom converters, we need to call .to_s on UUID model
objects.

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>