Don't overspecify successful status codes.

In HTTP, any 2xx status code indicates success. There were a number of
places in the documentation where a particular status code (e.g. 204
No Content) was specified as the only successful status code for a
particular request. That's overly-specific, and in some cases, wrong.

For example, consider a request like:

    GET /v1/account/container/object HTTP/1.1
    Range: bytes=20-50

The documentation before this change said that a 200 would be
returned. However, if the Range header is used, then the response may
have a 206 (Partial Content) status code instead.

There are other cases too, say 200 vs. 204, where either one works.

In general, Swift doesn't specify a particular response code for
successful responses; since Swift provides an HTTP API, it relies on
the HTTP standard to define "successful".

Change-Id: Ie21bcec491453f0371e4b84257aae4c30e342fb3
Merge "Don't overspecify successful status codes."