Added interop server, interop unit tests and fixes to pingpong
diff --git a/src/csharp/Grpc.IntegrationTesting/Grpc.IntegrationTesting.csproj b/src/csharp/Grpc.IntegrationTesting/Grpc.IntegrationTesting.csproj
index 9b46a64..e66f708 100644
--- a/src/csharp/Grpc.IntegrationTesting/Grpc.IntegrationTesting.csproj
+++ b/src/csharp/Grpc.IntegrationTesting/Grpc.IntegrationTesting.csproj
@@ -47,6 +47,8 @@
     <Compile Include="TestServiceGrpc.cs" />
     <Compile Include="Empty.cs" />
     <Compile Include="Messages.cs" />
+    <Compile Include="InteropClientServerTest.cs" />
+    <Compile Include="TestServiceImpl.cs" />
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
   <ItemGroup>