Wait for uncrypt to finish before rebooting

/system/bin/uncrypt needs to be triggered to prepare the OTA package
before rebooting into the recovery. For larger packages, uncrypt may be
killed before it finishes the work after the timeout. Change to monitor
the uncrypt status and show the progress to user.

Needs matching changes in bootable/recovery/uncrypt, system/core and
external/sepolicy.

Bug: 20012567
Bug: 20949086
Change-Id: I2348a98312c4dae81f618b45a2ee3b4cf6246ff5