azure: Move to vs2017-win2016 platform build host

Azure is moving to remove the vs2015-win2012r2 platform build host.  The
two suggested new platforms to use are vs2017-win2016 and windows-2019.
For now, move up to vs2017-win2016.

Cc: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
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I'm sending this as RFC as it fails to build for i686 but builds for
x86_64 and I'm out of my depth on fixing that.  Can you please take a
look Bin?  Thanks!