Support --set flag in deploy command

[jcorioland]

What this PR does / why we need it:
Brings support for using --set flag to override values from the api model JSON file directly from acs-engine deploy command

Ex:

acs-engine deploy --resource-group "your-resource-group" \
  --location "westeurope" \
  --subscription-id "your-subscription-id" \
  --api-model "./apimodel.json" \
  --set masterProfile.dnsPrefix="your-dns-prefix-override" \
  --set agentPoolProfiles[0].name="your-agentpool-0-name-override" \
  --set agentPoolProfiles[0].count=1 \
  --set linuxProfile.ssh.publicKeys[0].keyData="ssh-rsa PUBLICKEY azureuser@linuxvm" \
  --set servicePrincipalProfile.clientId="spn-client-id" \
  --set servicePrincipalProfile.secret="spn-client-secret"

Which issue this PR fixes: fixes #2796

Special notes for your reviewer:
I've done some refactoring in the deploy.go file to be able to extract the api model validation from the api model loading. That means that there is now 5 steps:

• validate the command line args
• merge the api model with eventual --set overrides into a new file
• load the merge api model
• validate the api model
• run the command

I think some code could be refactored more and shared between generate and deploy command, but it may be better to handle this in another issue/PR.

If applicable:

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

Release note:

Support for using --set flag to override api model JSON file directly in the acs-engine deploy command

[codecov]

Codecov Report

Merging #3188 into master will decrease coverage by 0.08%.
The diff coverage is 17.77%.

@@            Coverage Diff             @@
##           master    #3188      +/-   ##
==========================================
- Coverage   52.32%   52.24%   -0.09%     
==========================================
  Files         103      103              
  Lines       15452    15487      +35     
==========================================
+ Hits         8086     8091       +5     
- Misses       6638     6668      +30     
  Partials      728      728

[CecileRobertMichon]

What's the reason for changing this to true? See #3112

[jcorioland]

@CecileRobertMichon, good catch, no reason. It was a mistake. I've just fixed it. I've messed up with the generate command where we are loading the api model with validation. This is typically the "duplicated" code I was talking about that we need to find a way to share.

[acs-bot]

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[CecileRobertMichon]

lgtm