Add HSM support for kms encryption

[ritazh]

What this PR does / why we need it:

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

Special notes for your reviewer:

If applicable:

• documentation
• unit tests
• tested backward compatibility (ie. deploy with previous version, upgrade with this branch)

Release note:

[tariq1890]

@ritazh Can we add one pre-pull scripts for the kms docker image in the packer shell scripts?

Here: https://github.com/Azure/aks-engine/blob/b8f75fdff2e3d9b48e5480acc27a585efae0fed5/packer/install-dependencies.sh

[ritazh]

@tariq1890 the microsoft/k8s-azure-kms:v0.0.7 image is being pulled by the azure kms systemd service, not as part of the install-dependencies.sh script.

aks-engine/parts/k8s/artifacts/kubernetesazurekms.service

Line 16 in e98468e

microsoft/k8s-azure-kms:v0.0.7

So I don't think this image should be added there.

[tariq1890]

That's for the VHD so that the images are pre-pulled. Any VM that is created off of the VHD will already have that docker image in its local registry.

[tariq1890]

/lgtm

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[codecov]

Codecov Report

Merging #157 into master will decrease coverage by 0.02%.
The diff coverage is 14.28%.

@@            Coverage Diff             @@
##           master     #157      +/-   ##
==========================================
- Coverage   53.14%   53.11%   -0.03%     
==========================================
  Files          95       95              
  Lines       14216    14188      -28     
==========================================
- Hits         7555     7536      -19     
+ Misses       5992     5981      -11     
- Partials      669      671       +2

[codecov]

Codecov Report

Merging #157 into master will decrease coverage by 0.02%.
The diff coverage is 14.28%.

@@            Coverage Diff             @@
##           master     #157      +/-   ##
==========================================
- Coverage   53.14%   53.11%   -0.03%     
==========================================
  Files          95       95              
  Lines       14216    14188      -28     
==========================================
- Hits         7555     7536      -19     
+ Misses       5992     5981      -11     
- Partials      669      671       +2

[codecov]

Codecov Report

Merging #157 into master will decrease coverage by 0.02%.
The diff coverage is 14.28%.

@@            Coverage Diff             @@
##           master     #157      +/-   ##
==========================================
- Coverage   53.14%   53.11%   -0.03%     
==========================================
  Files          95       95              
  Lines       14216    14188      -28     
==========================================
- Hits         7555     7536      -19     
+ Misses       5992     5981      -11     
- Partials      669      671       +2