Avoid codesigning embedded assetpacks for AdHoc IPA

msbuild/Xamarin.iOS.Tasks.Core/Xamarin.iOS.Common.targets

@@ -1650,7 +1650,7 @@ Copyright (C) 2013-2016 Xamarin. All rights reserved.
 		<!-- Sign assetpacks -->
 		<Codesign
 			SessionId="$(BuildSessionId)"
-			Condition="'$(MtouchTargetsEnabled)' And '@(_AssetPack)' != ''"
+			Condition="'$(MtouchTargetsEnabled)' And '@(_AssetPack)' != '' And '$(_DistributionType)' == 'AppStore'"
 			ToolExe="$(CodesignExe)"
 			ToolPath="$(CodesignPath)"
 			CodesignAllocate="$(_CodesignAllocate)"