base: Test records for Zenodo

* Enables inveniomanage demosite populate with custom xml.
    
* NOTE: Before populating DB with demo records from custom xml
  please make sure that BASE_DEMOSITE_RECORDS_FIXTURE
  is set to list containing proper filenames


Signed-off-by: Adrian Pawel Baran <adrian.pawel.baran@cern.ch>
The original idea was to use `packages` argument. This function should have also `PendingDeprecation` warning as it's going to be replaced by new `uploader` (@egabancho).