Add power off & reboot to bootloader mode in advanced menu
Also:
Cleanup leftovers from previous poweroff option
Always ensure a clean reboot (Thanks to PhilZ for his implementation)

Bootloader option defaults to "bootloader" (fastboot mode), it can be overriden
by defining "ro.bootloader.mode=download" prop for samsung download mode
We leave reboot to bootloader option always enabled, that way we can
override the get_filtered_menu_selection bug that breaks the order
of the options when NULLifying menu options

Change-Id: Iec606ecc534ab147e424d30d75029a9f6e0c19f6