Incorrect config item in local_settings.py.example

The qos settings in horizon is not the same with
nova's.To fix it, modify the horizon
local_settings.py.example.

Change-Id: I1b31506e9b0e95be882edd490f3fa9dafe54abde
Closes-bug: #1324127
Merge "Incorrect config item in local_settings.py.example"