fix: continue upgrading after node drain error

[mboersma]

Reason for Change:
Doesn't return an error that occurs while draining a node during upgrade, just log it.

The idea here is that "cordon and drain" is the polite, best-effort way to upgrade, but that if it fails, upgrade can still delete the node and things will succeed with a bit more disruption to workloads.

Issue Fixed:
Fixes #1919

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[codecov]

Codecov Report

Merging #2013 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2013      +/-   ##
==========================================
+ Coverage   76.72%   76.73%   +<.01%     
==========================================
  Files         135      135              
  Lines       20574    20573       -1     
==========================================
  Hits        15786    15786              
+ Misses       3872     3871       -1     
  Partials      916      916

[jackfrancis]

/lgtm

[acs-bot]

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