tools/golang: Update xenlight.go to use generated code

    * Define missing libxl builtin types
    * Remove types that are now defined from gengotypes.py
    * Define fromC/toC for all builtin types
    * Add CreateDomain to demonstrate functioning generated code
    * Update any existing code so that compilation succeeds

Signed-off-by: Nick Rosbrook <rosbrookn@ainfosec.com>