Code review comment for lp:~brendan-donegan/checkbox/bug804190_server_sleep

Do we know how stable /sys/power/state is? how far back is it available, and is it likely to change in the future? I'm mainly asking since this is meant to be backported and it'd be good to know how likely we are to be affected by changes in this.

Other than this, I'm OK with merging this code.