Previously the proxy container controller could, in corner cases, get
into a loop while building a listing for a sharded container. For
example, if a root has a single shard then the proxy will be
redirected to that shard, but if that shard has shrunk into the root
then it will redirect the proxy back to the root, and so on until the
root is updated with the shard's shrunken status.
There is already a guard to prevent the proxy fetching shard ranges
again from the same container that it is *currently* querying for
listing parts. That deals with the case when a container fills in gaps
in its listing shard ranges with a reference to itself. This patch
extends that guard to prevent the proxy fetching shard ranges again
from any container that has previously been queried for listing parts.
Change-Id: I7dc793f0ec65236c1278fd93d6b1f17c2db98d7b
4539837647