CKAN version
2.9.x master at 93ef472

Describe the bug

The setting "pool_pre_ping" for the datastore connection is not working, because of a wrong setting key.

This is the code:

        config.setdefault('pool_pre_ping', True)
        engine = sqlalchemy.engine_from_config(config,
                                               'ckan.datastore.sqlalchemy.',
                                               **extras)

Since sqlachemy is told to read config keys with prefix ckan.datastore.sqlalchemy., the setting pool_pre_ping will not be taken into consideration.

Additional details

This issue is identical to #5932, but related to the datastore engine and not to the main ckan db.