Add option to keep generated files in _output/ for debugging

[PatrickLang]

Is this a request for help?: No

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Is this an ISSUE or FEATURE REQUEST? (choose one): Feature

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What version of acs-engine?: all

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Orchestrator and version (e.g. Kubernetes, DC/OS, Swarm): Kubernetes

What happened:

When you generate a template - there are some big big long strings for customData added to each VM. It's difficult to read these, and it's almost impossible to see how they'll be modified as you make changes to acs-engine.

I propose adding a new verbose flag that will output anything to a file for review before it's encoded into customData strings. That will make it easier to review changes to kubelet flags, apiserver settings and so on before running az group deploy

How to reproduce it (as minimally and precisely as possible):
acs-engine generate <anything.json>

[PatrickLang]

work in progress branch https://github.com/PatrickLang/acs-engine/tree/patricklang-3752

This is on the back burner, no ETA

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.