Fix #1483 -- [Battery - Linux] Fix AC status fetch
Fix #1483 -- [Battery - Linux] Fix AC status fetch

Fix a bug where the `online` property is checked inside battery
instead of AC.

As specified in issue #1483, `online` is found only inside
`/sys/class/power_supply/AC<x>/` directories, and equals `1` when cable is
plugged, and `0` when unplugged.

Edit: updated with --amend according to ZyX-I hints in order to work with
powerline daemon.

kenrachynski/powerline,prvnkumar/powerline,QuLogic/powerline,EricSB/powerline,blindFS/powerline,bezhermoso/powerline,QuLogic/powerline,areteix/powerline,QuLogic/powerline,areteix/powerline,EricSB/powerline,EricSB/powerline,blindFS/powerline,S0lll0s/powerline,kenrachynski/powerline,prvnkumar/powerline,prvnkumar/powerline,kenrachynski/powerline,blindFS/powerline,bezhermoso/powerline,S0lll0s/powerline,areteix/powerline,bezhermoso/powerline,S0lll0s/powerline