Fix manifest comparisons in new collection tests

Fix manifest comparisons in new collection tests

The previous version of these tests was comparing bound method objects
directly, rather than comparing the manifest texts returned by calling
them. Apparently in some setups this comparison returns True, but on my
development box it returns False, causing test failures. We haven't
fully diagnosed what causes the difference, but it seems clear enough
that comparing the method objects isn't the intent of these tests, but
rather they should compare the returned manifests. This commit updates
them to do so. No issue #.

Arvados-DCO-1.1-Signed-off-by: Brett Smith <brett.smith@curii.com>