bug 433736: Servlet 3.1 Compatibility 
https://bugs.eclipse.org/bugs/show_bug.cgi?id=433736

send HTTP 500 instead of 403, if IServletHelperService is not found

Change-Id: Ia2f4fd498b41a92a291b47de21818b531cb6d2e5
Signed-off-by: Judith Gull <jgu@bsiag.com>
Reviewed-on: https://git.eclipse.org/r/35327
Tested-by: Hudson CI