bpo-34582: Use new YAML syntax and agent pools for VSTS builds

[davidstaheli]

VSTS has new YAML syntax and agent pools available. This migrates to those. Specifically:

• queue --> pool
• Hosted Linux Preview --> Ubuntu 1604
• Hosted VS2017 --> VS2017-Win2016
• Hosted macOS Preview --> macOS 10.13

https://bugs.python.org/issue34582

[the-knights-who-say-ni]

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[davidstaheli]

@zooba FYI

[Mariatta]

Merge conflict. Please rebase.

[zooba]

Abandoning this PR - I've made a different set of changes to take advantage of the new syntax.