Move PullNupkgFilesFromBlob into FinalizeBuild.

Also, update dotnet/versions for the DotNetHost and NetCore.App packages.

Fix #3031

build_projects/dotnet-cli-build/NuGetUtil.cs

@@ -0,0 +1,32 @@
+using System.IO;
+using System.Reflection;
+using Microsoft.DotNet.Cli.Build.Framework;
+using NugetProgram = NuGet.CommandLine.XPlat.Program;
+
+namespace Microsoft.DotNet.Cli.Build
+{
+    public static class NuGetUtil
+    {
+        public static void PushPackages(string packagesPath, string destinationUrl, string apiKey)
+        {
+            int result = RunNuGetCommand(
+                "push",
+                "-s", destinationUrl,
+                "-k", apiKey,
+                Path.Combine(packagesPath, "*.nupkg"));
+
+            if (result != 0)
+            {
+                throw new BuildFailureException($"NuGet Push failed with exit code '{result}'.");
+            }
+        }
+
+        private static int RunNuGetCommand(params string[] nugetArgs)
+        {
+            var nugetAssembly = typeof(NugetProgram).GetTypeInfo().Assembly;
+            var mainMethod = nugetAssembly.EntryPoint;
+            return (int)mainMethod.Invoke(null, new object[] { nugetArgs });
+        }
+    }
+}
+