added dependency on Google.Apis.Auth package

...ationTesting.Client/Grpc.IntegrationTesting.Client.csproj

src/csharp/Grpc.IntegrationTesting.Client/app.config

...ationTesting.Server/Grpc.IntegrationTesting.Server.csproj

src/csharp/Grpc.IntegrationTesting.Server/app.config

...rp/Grpc.IntegrationTesting/Grpc.IntegrationTesting.csproj

src/csharp/Grpc.IntegrationTesting/app.config

src/csharp/Grpc.IntegrationTesting/packages.config