Refactor compute tests to not use _objectify()

During the objects conversion of nova-compute, we ended up with a lot of
places in the tests where we would take a dict or sqlalchemy object
and "objectify" it to pass it to a method that had been converted to
expect an obejct. That work is done now, but we have a LOT of cruft in
that code that needs to be cleaned up. This patch does that, and removes
the _objectify() helper.

Change-Id: Iee3e9ea619417178618f8f6c192097444899dd26
Merge "Refactor compute tests to not use _objectify()"