init: powerctl support and propagate longer canonical reboot reasons.

init: Received sys.powerctl='reboot,userrequested,recovery,ui' ... (/system/bin/recovery)
init: powerctl: unrecognized command 'reboot,userrequested,recovery,ui'

Test: manual & boot_reason_test.sh
Bug: 63736262
Bug: 135078366
Bug: 133326470
Change-Id: I931daf8dc4b74db5ee114c59ee215b1ba54bc31d