[Windows] Docker, .NET Core and NPM improvements (#3811)

* improve InitializeVM script

* Update windows2019.json

* remove configs

* resolve comments

* resolve comments; fix order

* fix templates

* move Node.js packages to toolset

* dotnet warmup and merge docker scripts

* Update Node.Tests.ps1

* Update Install-Docker.ps1

* fix node.js tests

* fix npm package installation

* Update Install-NodeLts.ps1

* fix tests

* fix test

images/win/scripts/Installers/Install-Docker.ps1

@@ -12,4 +12,15 @@ Start-Service docker
 Write-Host "Install-Package Docker-Compose"
 Choco-Install -PackageName docker-compose
 
-Invoke-PesterTests -TestFile "Docker" -TestName "Docker"
+$dockerImages = (Get-ToolsetContent).docker.images
+foreach ($dockerImage in $dockerImages) {
+    Write-Host "Pulling docker image $dockerImage ..."
+    docker pull $dockerImage
+
+    if (!$?) {
+        Write-Host "Docker pull failed with a non-zero exit code"
+        exit 1
+    }
+}
+
+Invoke-PesterTests -TestFile "Docker"