Make the launcher exit on boot completed/failed

By default the launcher behaves as usual (blocking until the device is
stopped), but when given the --daemon flag it forks after doing the
necessary preprocessing and launches everything in background, exiting
once it gets the boot completed or failed signal.

Bug: 111307422
Test: local
Change-Id: I6a2f48df70c878d3f1b2bdf671770730e935e7c0