Fix import_json_tests
Fixes to import_akomantoso_tests
Fix search index calls to affect test database

as call_command uses the django config, we'd need to pass in
an appropriate settings object, which seems faffy.

Instead, we just call the EntityNameIndex and clear/update it,
matching the process for a rebuild.

(requires mysociety/popit-resolver@5f8a859d32755fa7f3e0aa0dedef247337863d67)
Restrict search tests to SpeechIndex
Fix errors in populate_speakers_command_tests