[frontend] Redis.setex swapped arguments in v3+
    
    To avoid additional version checking/API checking, require the use
    of external StrictRedis object which has a consistent setex() API
    across redispy v2/3.
    
    Per upstream docs:
    2.X users that are using the Redis class will have to make
    changes if they use any of the following commands:
    - SETEX: The argument order has changed. The new order is (name,
    time, value).
    
    Fixes: #589, #602