fix reference to bouncyCastles assembly

src/csharp/Grpc.IntegrationTesting/Grpc.IntegrationTesting.csproj

@@ -31,6 +31,9 @@
     <PlatformTarget>AnyCPU</PlatformTarget>
   </PropertyGroup>
   <ItemGroup>
+    <Reference Include="BouncyCastle.Crypto">
+      <HintPath>..\packages\BouncyCastle.1.7.0\lib\Net40-Client\BouncyCastle.Crypto.dll</HintPath>
+    </Reference>
     <Reference Include="Google.Apis.Auth, Version=1.9.2.27817, Culture=neutral, PublicKeyToken=4b01fa6e34db77ab, processorArchitecture=MSIL">
       <SpecificVersion>False</SpecificVersion>
       <HintPath>..\packages\Google.Apis.Auth.1.9.2\lib\net40\Google.Apis.Auth.dll</HintPath>

src/csharp/Grpc.IntegrationTesting/packages.config

 <?xml version="1.0" encoding="utf-8"?>
 <packages>
+  <package id="BouncyCastle" version="1.7.0" targetFramework="net45" />
   <package id="Google.Apis.Auth" version="1.9.2" targetFramework="net45" />
   <package id="Google.Apis.Core" version="1.9.2" targetFramework="net45" />
   <package id="Google.ProtocolBuffers" version="2.4.1.521" targetFramework="net45" />