[xharness] Use Xcode 8 when debugging.

tests/xharness/xharness.csproj

@@ -20,7 +20,7 @@
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
     <ConsolePause>false</ConsolePause>
-    <Commandlineparameters>--verbose --jenkins --autoconf --rootdir ../ --sdkroot /Applications/Xcode73.app</Commandlineparameters>
+    <Commandlineparameters>--verbose --jenkins --autoconf --rootdir ../ --sdkroot /Applications/Xcode8-beta1.app</Commandlineparameters>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
     <DebugType>full</DebugType>