FixingElevated CPU utilization on one node when using RedisCluster pipeline

[shchurov]

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Description of change

This PR addresses the issue #1932.
The current implementation creates a new instance of CommandsParser for every ClusterPipeline instance. It may get expensive because CommandsParser executes COMMAND command during the initialization. I assume that pipelines can reuse the parser instance from RedisCluster instead.

[codecov-commenter]

Codecov Report

Merging #1985 (a4ed092) into master (aafa7f1) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1985      +/-   ##
==========================================
- Coverage   93.04%   93.03%   -0.02%     
==========================================
  Files          77       77              
  Lines       16603    16603              
==========================================
- Hits        15449    15447       -2     
- Misses       1154     1156       +2     

Impacted Files	Coverage Δ
redis/cluster.py	92.42% <100.00%> (ø)
tests/test_cluster.py	98.16% <0.00%> (-0.13%)	⬇️

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[chayim]

Awesome @shchurov thank you for the PR and for fixing the bug you reported. I just merged in the latest master- it all passes, and we'll merge this in.