chore: rev Linux VHDs to 2019.12.11

[jackfrancis]

Reason for Change:

Includes the following additive pre-downloaded container images:

• k8s.gcr.io/hyperkube-amd64:v1.16.4
• k8s.gcr.io/hyperkube-amd64:v1.15.7
• k8s.gcr.io/cloud-controller-manager-amd64:v1.15.7

Issue Fixed:

Requirements:

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

Notes:

[codecov]

Codecov Report

Merging #2451 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #2451   +/-   ##
======================================
  Coverage    72.3%   72.3%           
======================================
  Files         130     130           
  Lines       23648   23648           
======================================
  Hits        17098   17098           
  Misses       5524    5524           
  Partials     1026    1026

[marosset]

/lgtm

[acs-bot]

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