The proxy may use a sub-request to fetch a container listing response,
for example for updating shard ranges. If it then fails to parse the
response, it should use the sub-request path when logging a warning or
error. Before, the proxy would use the original request path which may
have been to an object.
Change-Id: Id904f4cc0f911f9e6e53d4b3ad7f98aacd2b335d
130377bd27