Error handling API was broken in analytics 7.1.0-2256

SDKs expect that "status" field will always be rendered in JSON payload of the service reseponse. It seems like recent changes in rendering errors, changed the shape of the payload from plain text to JSON, but the new structure was not discussed/reviewed by SDK team representative.

This is our specification for analytics service, and it states that status is not optional field.
https://github.com/couchbaselabs/sdk-rfcs/blob/master/rfc/0057-sdk3-analytics.md#analyticsresult

Previous versions were rendering some errors as plain text, and the SDKs adapted to parse that representation. Error handling is critical component of the SDKs, and we expect to be notified about any changes in the on-the-wire message representation.