we make the index assertion db independant so it is a noop for
a future native sql backend. This allows us to reuse even more
tests for the different db architectures.
This commit starts reusing test cases which are not dependant on
the kv db backend. So they can be later used with the native db
implementation as well.
This commit moves most of the code into its own package. It is
the smallest code move possible without moving import cycles and
keeping the changes to the code base as small as possible during
refactor.
