chore: update Linux VHDs to 2020.09.08

[jackfrancis]

Reason for Change:

Updates Linux VHDs to version 2020.09.08 for both Ubuntu 16.04-LTS and 18.04-LTS. These images include the "generate aggregated API certs" script pre-installed to save on cloud-init payload overhead.

Issue Fixed:

Requirements:

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

Notes:

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jackfrancis

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• OWNERS [jackfrancis]

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[codecov]

Codecov Report

Merging #3811 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3811      +/-   ##
==========================================
+ Coverage   73.20%   73.21%   +0.01%     
==========================================
  Files         148      148              
  Lines       25385    25385              
==========================================
+ Hits        18583    18586       +3     
+ Misses       5666     5663       -3     
  Partials     1136     1136              

Impacted Files	Coverage Δ
pkg/engine/templates_generated.go	53.42% <0.00%> (ø)
pkg/engine/engine.go	86.09% <0.00%> (+0.35%)	⬆️

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