add kill all for shutdown_timeout of 0

- If it is explicitly set to 0, active processes can block
  umount completely. Safe to kill all processes and umount.
- also add additional sync after emulated partition umount
  as that can change /data partition files

bug: 36004738
Test: many reboots

Change-Id: I6c9b07b6fdece44b9caec4e45ecf26a20d0eb96e