When responding to a GET request for a manifest, it was intended that
the proxy server lazily fetch the pieces of the container
listing. That way, a single client request doesn't immediately turn
into a bunch of requests to backends. The additional requests should
only get made if the client is putting in the work of receiving the
object body.
However, commit 156f27c accidentally changed this so that all the
pieces of the container listing are eagerly fetched up-front. Better
yet, if an object has more than CONTAINER_LISTING_LIMIT (default
10,000) segments, the container listing is then fetched a second time,
albeit lazily, while streaming out the response.
This commit restores the laziness and adds tests for it.
Change-Id: I49840a7059e6f999ce19199ecb10cdb77358526b
83bbd0aef2