Fix python install and bump to 3.6.6

Summary:
The python installer cannot be downloaded at the moment because it uses TLS 1.2

This patch allows TLS 1.2 download and changes the method used to match what is used in the rest of the code.

BUG: 394644

Reviewers: vonreth, #craft

Reviewed By: vonreth, #craft

Tags: #craft

Differential Revision: https://phabricator.kde.org/D15849