Opens a database specified by the parameters from parse_options().

def open_database(parameters):
    """Opens a database specified by the parameters from parse_options()."""
    spanner_client = spanner.Client()
    instance_id = parameters['cloudspanner.instance']
    instance = spanner_client.instance(instance_id)
    database_id = parameters['cloudspanner.database']
    pool = spanner.BurstyPool(int(parameters['num_worker']))
    database = instance.database(database_id, pool=pool)

    return database