Retry on error exception and timeout fixes

[barshaul]

…onError import

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Description of change

1. Added timeout error to the list of errors to retry.
2. Changed TimeoutError import from redis.exception to RedisTimeoutError so python's TimeoutError won't get override, as it can be also thrown when we try to establish a connection.
3. A ConnectionError import was added from redis.exceptions, since it was mistakenly not imported and the default ConnectionError was being used.
4. Increased sleep time to 0.25sec when ClusterDownError is thrown, so it will let more time for the cluster to get healed.

[codecov-commenter]

Codecov Report

Merging #1821 (c58d82b) into master (4831034) will increase coverage by 0.07%.
The diff coverage is 91.30%.

@@            Coverage Diff             @@
##           master    #1821      +/-   ##
==========================================
+ Coverage   94.32%   94.40%   +0.07%     
==========================================
  Files          75       75              
  Lines       15783    15771      -12     
==========================================
+ Hits        14887    14888       +1     
+ Misses        896      883      -13     

Impacted Files	Coverage Δ
redis/cluster.py	92.13% <88.23%> (+1.83%)	⬆️
tests/test_cluster.py	98.79% <100.00%> (-0.01%)	⬇️
tests/conftest.py	90.14% <0.00%> (-0.99%)	⬇️

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[chayim]

TimeoutError vs RedisTimeoutError - see below.