healthcheck.pl: check_reboot_required
healthcheck.pl: check_reboot_required

- Checks if a reboot.required file is present - error if YES
Closes #960

mschlenstedt/Loxberry,mschlenstedt/Loxberry,mschlenstedt/Loxberry,mschlenstedt/Loxberry,mschlenstedt/Loxberry,mschlenstedt/Loxberry