Merge Nuget changes

Fix pack
Move dotnet-nuget to NuGetForwardingApp [tests will need to be fixed]

src/dotnet/NuGetForwardingApp.cs

@@ -0,0 +1,42 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using Microsoft.DotNet.Cli;
+
+namespace Microsoft.DotNet.Tools
+{
+    public class NuGetForwardingApp
+    {
+        private const string s_nugetExeName = "NuGet.CommandLine.XPlat.dll";
+        private readonly ForwardingApp _forwardingApp;
+
+        public NuGetForwardingApp(IEnumerable<string> argsToForward)
+        {
+            _forwardingApp = new ForwardingApp(
+                GetNuGetExePath(),
+                argsToForward);
+        }
+
+        public int Execute()
+        {
+            return _forwardingApp.Execute();
+        }
+
+        public NuGetForwardingApp WithEnvironmentVariable(string name, string value)
+        {
+            _forwardingApp.WithEnvironmentVariable(name, value);
+
+            return this;
+        }
+
+        private static string GetNuGetExePath()
+        {
+            return Path.Combine(
+                AppContext.BaseDirectory,
+                s_nugetExeName);
+        }
+    }
+}