Support CF.MEXISTS + Clean bf/commands.py

[Avital-Fine]

Pull Request check-list

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• Does $ tox pass with this change (including linting)?
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Description of change

Closes #2181

[dvora-h]

Also - linters fails

[codecov-commenter]

Codecov Report

Merging #2184 (cace8fd) into master (8a1feb3) will increase coverage by 0.00%.
The diff coverage is 92.59%.

@@           Coverage Diff           @@
##           master    #2184   +/-   ##
=======================================
  Coverage   91.99%   91.99%           
=======================================
  Files         108      108           
  Lines       27398    27373   -25     
=======================================
- Hits        25204    25183   -21     
+ Misses       2194     2190    -4     

Impacted Files	Coverage Δ
redis/commands/bf/commands.py	98.86% <92.30%> (+0.84%)	⬆️
tests/test_bloom.py	99.56% <100.00%> (+<0.01%)	⬆️
tests/test_cluster.py	97.02% <0.00%> (+0.11%)	⬆️

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