Also first try to download it from local mirror.
This install script appears to be doing a lot of git-cloning and downloading
itself though, so it is still far from the ideal solution: to only download
from locally cached endpoints.
Task-number: QTQAINFRA-3134
Change-Id: I32131045d6e62f302ec666b4ac055ca5ee9662d5
Reviewed-by: Heikki Halmet <heikki.halmet@qt.io>