Due to year-long unreliability.
The default Ubuntu mirror works as fast as the Azure one when it's
working at its normal speed. And has HTTPS.
Also:
- replac the retry hack that turn out to not solve the problem.
- add timeouts to each download step to catch slowness early.
Follow-up to a5838847c4#21181
Follow-up to 5172ba5475#21107Closes#21414