Piotrp msft/msbuild/incremental test (#3842)

* Incremental Testing - Part 1

* Fix 'clean' bug

* Remove --fallbacksource from TestAssetPackage restore.

build_projects/dotnet-cli-build/DotNetPack.cs

@@ -0,0 +1,90 @@
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+
+namespace Microsoft.DotNet.Cli.Build
+{
+    public class DotNetPack : DotNetTool
+    {
+        protected override string Command
+        {
+            get { return "pack"; }
+        }
+
+        protected override string Args
+        {
+            get { return $"{GetProjectPath()} {GetConfiguration()} {GetNoBuild()} {GetBuildBasePath()} {GetOutput()} {GetVersionSuffix()}"; }
+        }
+
+        public string Configuration { get; set; }
+
+        public bool NoBuild { get; set; }
+
+        public string BuildBasePath { get; set; }
+
+        public string Output { get; set; }
+
+        public string ProjectPath { get; set; }
+
+        public string VersionSuffix { get; set; }
+
+        private string GetConfiguration()
+        {
+            if (!string.IsNullOrEmpty(Configuration))
+            {
+                return $"--configuration {Configuration}";
+            }
+
+            return null;
+        }
+
+        private string GetNoBuild()
+        {
+            if (NoBuild)
+            {
+                return $"--no-build";
+            }
+
+            return null;
+        }
+
+        private string GetBuildBasePath()
+        {
+            if (!string.IsNullOrEmpty(BuildBasePath))
+            {
+                return $"--build-base-path {BuildBasePath}";
+            }
+
+            return null;
+        }
+
+        private string GetOutput()
+        {
+            if (!string.IsNullOrEmpty(Output))
+            {
+                return $"--output {Output}";
+            }
+
+            return null;
+        }
+
+        private string GetProjectPath()
+        {
+            if (!string.IsNullOrEmpty(ProjectPath))
+            {
+                return $"{ProjectPath}";
+            }
+
+            return null;
+        }
+
+        private string GetVersionSuffix()
+        {
+            if (!string.IsNullOrEmpty(VersionSuffix))
+            {
+                return $"--version-suffix {VersionSuffix}";
+            }
+
+            return null;
+        }
+    }
+}