arch_updates: Better error handling when no internet connection
arch_updates: Better error handling when no internet connection

This fixes the exception that occurs when the module runs without an
internet connection. It also reworks the two methods (pacman, aur) of
update-checking to differentiate between 0 updates and errors (when
there is no internet connection).

Andrwe/py3status,valdur55/py3status,ultrabug/py3status,valdur55/py3status,ultrabug/py3status,ultrabug/py3status,tobes/py3status,tobes/py3status,valdur55/py3status,guiniol/py3status,Andrwe/py3status,guiniol/py3status