Add Azure Stack Support so that Azure Key Vaults can be used inside Azure stack.

[jselleck]

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This issue is a: (mark with an x)

• bug report
• request for new sample
• documentation issue or request
• regression (a behavior that used to work and stopped in a new release)

Steps to reproduce:

Since the azure key vault url is hard coded you cannot use the sample as is for azure stack key vault.

Errors and log messages:

Expected behavior:

User should specify a vault url instead of a vault.

OS and Go versions:

Further info: