`Arq` has ability to retry connections to redis in case of problems.
That is a nice feature, but it crashes after hundreds of attempts
reaching maximal recursion depth. This change modifies re-try algorithm
from recursion to iteration avoiding the limit.

In practice it would be nice to have ability to wait forever as issue
with redis instance should not kill worker process, but that is a
separate change that can be built on top.

Fixes exception when retrying redis connection many times:
  RecursionError: maximum recursion depth exceeded while getting the str of an object