Fireworks error messages no longer degrade to HTTP reason phrase

Patch Changes

• b42ee57: Parse the object error envelope Fireworks actually returns ({"error":{"object","type","code","message"}}) instead of a bare string. The mismatched schema failed to parse, so error messages silently degraded to the HTTP reason phrase — Bad Request over HTTP/1.1, and an empty string over HTTP/2, which has no reason phrase. Fireworks' own message now reaches the caller, e.g. Model not found, inaccessible, and/or not deployed rather than Not Found.