Adds reference to Utilities assembly so VSSDK works

VSTestHost/VSTestHost.csproj

@@ -84,6 +84,7 @@
     <When Condition="$(VSTarget) == '15.0'">
       <ItemGroup>
         <Reference Include="Microsoft.VisualStudio.Shell.Framework, Version=$(VSTarget).0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
+        <Reference Include="Microsoft.VisualStudio.Utilities, Version=$(VSTarget).0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL" />
       </ItemGroup>
     </When>
     <Otherwise>