Modify dotnet-test to run testRunner for all tfms

Fixes #2506

TestAssets/TestProjects/ProjectsWithTests/NetCoreAppOnlyProject/GivenThatIWantSomeFakeTests.cs

@@ -0,0 +1,22 @@
+// 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 Xunit;
+
+namespace FakeTests
+{
+    public class GivenThatIWantSomeFakeTests
+    {
+        [Fact]
+        public void It_succeeds()
+        {
+            Assert.True(true);
+        }
+
+        [Fact]
+        public void It_also_succeeds()
+        {
+            Assert.True(true);
+        }
+    }
+}

TestAssets/TestProjects/ProjectsWithTests/NetCoreAppOnlyProject/project.json

@@ -0,0 +1,23 @@
+{
+  "version": "1.0.0-*",
+  "dependencies": {
+    "Microsoft.NETCore.App": {
+      "type": "platform",
+      "version": "1.0.0-rc2-*"
+    },
+    "System.Linq.Expressions": "4.0.11-rc2-24022",
+    "System.Runtime.Serialization.Primitives": "4.1.1-rc2-24022",
+    "xunit": "2.1.0",
+    "dotnet-test-xunit": "1.0.0-rc2-162081-13"
+  },
+  "frameworks": {
+    "netcoreapp1.0": {
+      "imports": [
+        "netstandardapp1.5",
+        "dnxcore50",
+        "portable-net45+win8"
+      ]
+    }
+  },
+  "testRunner": "xunit"
+}