Remove index creation form _init_, declare public method

suitcase/mongo_normalized/__init__.py

@@ -83,9 +83,8 @@ def __init__(
  self._asset_registry_db = assets_db
  self._ignore_duplicates = ignore_duplicates
  self._resource_uid_unique = resource_uid_unique
- self._create_indexes()
 
- def _create_indexes(self):
+ def create_indexes(self):
  """
  Create indexes on the various collections.