Checks if the specified bank contains the specified key.

def contains(bank, key):
    '''
    Checks if the specified bank contains the specified key.
    '''
    redis_server = _get_redis_server()
    bank_redis_key = _get_bank_redis_key(bank)
    try:
        return redis_server.sismember(bank_redis_key, key)
    except (RedisConnectionError, RedisResponseError) as rerr:
        mesg = 'Cannot retrieve the Redis cache key {rkey}: {rerr}'.format(rkey=bank_redis_key,
                                                                           rerr=rerr)
        log.error(mesg)
        raise SaltCacheError(mesg)