[COOK-4728] Allow reboot handler as exception handler

Add the allow_reboot_on_failure attribute to register the
WindowsRebootHandler as an exception handler too, to allow performing
reboots even if the Chef run fails. This is nice to have and reduces the
risk of dropping reboot requests.
Merge pull request #81 from criteo-cookbooks/COOK-4728

[COOK-4728] Allow reboot handler as exception handler