When the user specified caching plugin doesn't initialize correctly, we
were falling back to a dict. however, dicts do not have the same
update() method as the FactCache. We use the update method when we
update a cache with a subsequent value. So when that combination of
things happened, the code would traceback.
In devel, we made this change to fix things: https://github.com/ansible/ansible/pull/49516
but that involves several deprecations. So we're doing this smaller
hack in 2.7 to fix the traceback without introducing those deprecations
in a stable release.
