Includes slowlog complexity info if available

[ian28223]

Pull Request check-list

• Does $ tox pass with this change (including linting)?
• Does travis tests pass with this change (enable it first in your forked repo and wait for the travis build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?

NOTE: these things are not required to open a PR and can be done
afterwards / while the PR is open.

Description of change

Includes complexity info from item[3] if command is in item[4]

Based on #622
tests copied from above PR

[codecov-commenter]

Codecov Report

Merging #1489 (f904b47) into master (bc58542) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1489      +/-   ##
==========================================
+ Coverage   86.58%   86.61%   +0.03%     
==========================================
  Files           7        7              
  Lines        2914     2921       +7     
==========================================
+ Hits         2523     2530       +7     
  Misses        391      391              

Impacted Files	Coverage Δ
redis/client.py	87.07% <100.00%> (+0.04%)	⬆️

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[ian28223]

@andymccurdy Sorry for tagging you here but I couldn't find anyone else to review

[chayim]

@andymccurdy Sorry for tagging you here but I couldn't find anyone else to review

@ian28223 I assigned it to myself to have a look. I'll likely do so Sunday.

[chayim]

@ian28223 Thanks a tonne for this contribution! It looks like a great addition to redis-py support for Redis Enterprise. For curious future readers here are some docs.