(maint) Setup Windows container build env

 - Add Azure Pipelines invocation to enable environment setup
 - Relies on puppet_docker_tools 0.2.0+ which has removed calls to
   the docker-api gem and replaced them with vanilla docker command
   invocations, so as to support Windows

azure-pipelines.yml

@@ -46,3 +46,8 @@ steps:
     Get-ChildItem Env: | % { Write-Host "$($_.Key): $($_.Value)"  }
   displayName: Diagnostic Host Information
   name: hostinfo
+- powershell: |
+    . ./docker/ci/build.ps1
+    Invoke-ContainerBuildSetup
+  displayName: Prepare Build Environment
+  name: build_prepare

docker/ci/build.ps1

@@ -0,0 +1,16 @@
+$ErrorActionPreference = 'Stop'
+
+function Get-CurrentDirectory
+{
+  $thisName = $MyInvocation.MyCommand.Name
+  [IO.Path]::GetDirectoryName((Get-Content function:$thisName).File)
+}
+
+# installs gems for build and test and grabs base images
+function Invoke-ContainerBuildSetup
+{
+  Push-Location (Get-CurrentDirectory)
+  bundle install --path '.bundle/gems'
+  bundle exec puppet-docker update-base-images ubuntu:16.04
+  Pop-Location
+}