core: make exception handling slightly more sane
core: make exception handling slightly more sane

Before, this did:

2020-04-18 09:32:08,818 libqtile manager.py:<lambda>():L250  Got an exception in poll loop
NoneType: None

Now it does:

2020-04-18 09:42:05,627 libqtile manager.py:handle_exception():L124  [Errno 2] No such file or directory: 'xbacklight'

It would be better if we could get a stack trace, but I don't see a good
way of doing that right now. Hopefully they'll add it in the future, but at
least this prints the exception :)

Signed-off-by: Tycho Andersen <6b523322678240882acbb4da5312a12d8cd0082d@tycho.ws>

zordsdavini/qtile,zordsdavini/qtile