Test directory refactoring step 1.

Moving TestProjects and TestPackages under root 'TestAssets' folder.

Partial fix #1250

TestAssets/TestProjects/TestAppCompilationContext/Program.cs

@@ -0,0 +1,17 @@
+// 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.Diagnostics;
+
+namespace TestApp
+{
+    public class Program
+    {
+        public static int Main(string[] args)
+        {
+            Console.WriteLine(TestLibrary.Helper.GetMessage());
+            return 100;
+        }
+    }
+}

TestAssets/TestProjects/TestAppCompilationContext/project.json

@@ -0,0 +1,22 @@
+{
+    "version": "1.0.0-*",
+    "compilationOptions": {
+        "emitEntryPoint": true,
+        "preserveCompilationContext": true
+    },
+
+    "dependencies": {
+        "TestLibrary": "1.0.0-*",
+
+        "NETStandard.Library": "1.0.0-rc2-23805"
+    },
+
+    "frameworks": {
+        "dnxcore50": { }
+    },
+
+    "scripts": {
+        "prepublish" : ["echo prepublish_output ?%publish:ProjectPath%? ?%publish:Configuration%? ?%publish:OutputPath%? ?%publish:Framework%? ?%publish:Runtime%?"],
+        "postpublish" : ["echo postpublish_output ?%publish:ProjectPath%? ?%publish:Configuration%? ?%publish:OutputPath%? ?%publish:Framework%? ?%publish:Runtime%?"]
+    }
+}