chore: update cluster-autoscaler for 1.15 and 1.16

[mboersma]

Reason for Change:
See https://github.com/kubernetes/autoscaler/releases/tag/cluster-autoscaler-1.15.5
and https://github.com/kubernetes/autoscaler/releases/tag/cluster-autoscaler-1.16.4

Looks like a backport of what we merged already for 1.17 in #2730.

Issue Fixed:

Requirements:

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

Notes:

[codecov]

Codecov Report

Merging #2776 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2776   +/-   ##
=======================================
  Coverage   72.35%   72.35%           
=======================================
  Files         137      137           
  Lines       25341    25341           
=======================================
  Hits        18335    18335           
  Misses       5949     5949           
  Partials     1057     1057

[jackfrancis]

/lgtm

[acs-bot]

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