Fix KeyError on Storage Policy Container Sync

In the proxy, container_info can return a 'storage_policy' of None.  When
you set a header value on a swob.Request to None that effectively just
delete's the key.  One path through the proxy during container sync was
counting on the the 'X-Backend-Storage-Policy-Index' being set which isn't
the case if the cached container_info if for a pre-policies container.

Also clean up some test cruft, tighten up the interface on FakeConn, and add
some object controller tests to exercise more interesting failure and handoff
code paths.

Change-Id: I643e08c208efdc5a39e840d9e96710ddad54236b