test/rgw: zone_cloud: deal with key representation and other fixes

test/rgw: zone_cloud: deal with key representation and other fixes

Needed to present a key to the tests that reflected its original name
and version_id (and etag), so that the callers don't need to be modified.
However, this can only be achieved if we get the key, which doesn't work
if the caller was just listing the bucket objects. Created a new CloudKey
class to deal with the different issues there.
Also, other test related fixes.

Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>