Throw Command Unknown for dependency tools in libraries. (#2933)

* Throw Command Unknown for dependency tools in libraries.

* Add testProjects to test tools command for libraries.

* update failing tests

* Add tests verifying that dependency tools are not available in libraries

TestAssets/DesktopTestProjects/LibraryWithDirectDependencyDesktopAndPortable/Program.cs

@@ -0,0 +1,12 @@
+using System;
+
+namespace ConsoleApplication
+{
+    public class Program
+    {
+        public static void Main(string[] args)
+        {
+            Console.WriteLine("Hello World!");
+        }
+    }
+}

TestAssets/DesktopTestProjects/LibraryWithDirectDependencyDesktopAndPortable/project.json

@@ -0,0 +1,31 @@
+{
+  "version": "1.0.0-*",
+  "compilationOptions": {
+    "emitEntryPoint": false
+  },
+  "dependencies": {
+    "dotnet-desktop-and-portable": "1.0.0-*"
+  },
+  "frameworks": {
+    "netstandard1.5": {
+      "dependencies": {
+        "NETStandard.Library": "1.5.0-rc2-24027"
+      },
+      "imports": [
+        "portable-net45+win8",
+        "dnxcore50",
+        "netcoreapp1.0"
+      ]
+    },
+    "net451": {}
+  },
+  "tools": {
+    "dotnet-dependency-tool-invoker": {
+      "version": "1.0.0-*",
+      "imports": [
+        "dnxcore50",
+        "portable-net45+win8"
+      ]
+    }
+  }
+}