Fix ClusterMetadata request_update()

[jackgene]

Changes

Fixes #1055

• Call Future#set_result(...) instead of Future#success(...)
• Call Future#set_exception(...) instead of Future#failure(...).
• Added unit tests to demonstrate original error, and verify fix.

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> (e.g. 588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the PR
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: Fix issue with non-ascii contents in doctest text files.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.08%. Comparing base (01c60cd) to head (3fe7787).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1056      +/-   ##
==========================================
+ Coverage   95.02%   95.08%   +0.06%     
==========================================
  Files         114      114              
  Lines       16971    16982      +11     
  Branches     2771     1763    -1008     
==========================================
+ Hits        16126    16147      +21     
+ Misses        497      487      -10     
  Partials      348      348              

Flag	Coverage Δ
cext	92.04% <100.00%> (+0.11%)	⬆️
integration	94.77% <100.00%> (+0.09%)	⬆️
purepy	94.59% <100.00%> (+0.09%)	⬆️
unit	52.99% <100.00%> (+0.11%)	⬆️

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