Previously, if you called get_account_info, get_container_info, or
get_object_info, then the results of that call would be cached in the
WSGI environment as top-level keys. This is okay, except that if you,
in middleware, copy the WSGI environment and then make a subrequest
using the copy, information retrieved in the subrequest is cached
only in the copy and not in the original. This can mean lots of extra
trips to memcache for, say, SLO validation where the segments are in
another container; the object HEAD ends up getting container info for
the segment container, but then the next object HEAD gets it again.
This commit moves the cache for get_*_info into a dictionary at
environ['swift.infocache']; this way, you can shallow-copy the request
environment and still get the benefits from the cache.
Change-Id: I3481b38b41c33cd1e39e19baab56193c5f9bf6ac
ce90a1e79e