Change abortChanges to take a message and bool

abortChanges will attempt to pass a reboot message, and will only reboot
if the device is currently checkpointing. Additionally, it can opt to
attempt to prevent future attempts. This only works for non-bootloader
controlled updates. Failures are ignored, as it will always reboot the
device. In the unlikely event of such a failure, the device will
continue to retry as though you did not ask to prevent future attempts.

Test: vdc checkpoint abortChanges abort_retry_test 1
      vdc checkpoint abortChanges abort_noretry_test 0

Change-Id: I7b6214765a1faaf4fd193c73331696b53ae572d2