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>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/.azure-pipelines.yml b/.azure-pipelines.yml
index 916ab84..a0713dd 100644
--- a/.azure-pipelines.yml
+++ b/.azure-pipelines.yml
@@ -1,5 +1,5 @@
 variables:
-  windows_vm: vs2015-win2012r2
+  windows_vm: vs2017-win2016
   ubuntu_vm: ubuntu-18.04
   ci_runner_image: trini/u-boot-gitlab-ci-runner:bionic-20200112-17Jan2020
   # Add '-u 0' options for Azure pipelines, otherwise we get "permission