light refactor of engine.go

[jackfrancis]

What this PR does / why we need it:

• moves all constants under acsengine package to pkg/acsengine/const.go
• ditto for types to pkg/acsengine/types.go
• eliminates unnecessary exportable (uppercase first letter) package references
• slight reorganization of func placements in engine.go (exportable at top, private below)
• ARM parameters-specific foo is now in pkg/acsengine/params.go and pkg/acsengine/params_k8s.go (broken out from engine.go)
• ARM template generation-specific foo is now in pkg/acsengine/template_generator.go (broken out from engine.go)

The obvious practical benefits are to reduce engine.go by ~1700 lines and to make unit test // TODO work a little more approachable.

There is no functional intent of this PR, any such observations would disqualify 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:

light refactor of engine.go

[acs-bot]

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[codecov]

Codecov Report

Merging #3084 into master will increase coverage by 0.01%.
The diff coverage is 57.57%.

@@            Coverage Diff             @@
##           master    #3084      +/-   ##
==========================================
+ Coverage   51.85%   51.87%   +0.01%     
==========================================
  Files          99      102       +3     
  Lines       15193    15197       +4     
==========================================
+ Hits         7879     7883       +4     
  Misses       6590     6590              
  Partials      724      724

[CecileRobertMichon]

"light" 😛

[jackfrancis]

@jim-minter @pweil- For your consideration. There is some shared surface area here and will wait for your sign-off. This PR is of the "eat your spinach" variety: a little bit of tech-debt payback within the confines of an easily reviewable PR. (basically the length of a flight between PDX and SEA, which is not long enough to allow for too much change :) )

[CecileRobertMichon]

lgtm

[serbrech]

As much as I wanted to take on this, I don't think it was possible for someone else than you guys to tackle it. Awesome 🚀