advanced reboot: add soft reboot option

adds a "soft reboot" option which restarts zygote

Signed-off-by: Roman Birg <roman@cyngn.com>
Signed-off-by: Humberto Borba <humberos@gmail.com>

Change-Id: Ia6e5ed9b053e1c5ebd1fc55e5692858b97f7e0fc