Improvements to report exp/imp tests

With the new reports import/export additions some minor errors were made to
correcting the stored config based export/import tests. In particular we were
inserting store-report => 1 into the metadata to make a test pass.

Instead of doing that, I've modified the compare_export_data test to allow
us to control what exactly gets compared, so we can exclude the metadata
comparison if required.

I've also refactored compare_export_data a tad as previously it didn't have
its own compare_report method or report munging facility - it was using the
metadata one instead.

Signed-off-by: Ken Barber <ken@bob.sh>