Upgrade Tor Browser to 8.0a10

It’s not the final 8.0 but better detect now any breakage or adjustment we need to do on our side.

• announce: https://lists.torproject.org/pipermail/tor-qa/2018-August/000947.html
• known issues: https://trac.torproject.org/projects/tor/query?status=!closed&keywords=~ff60-esr&max=256

Feature Branch: feature/15803-tor-browser-8.0a10+force-all-tests

Related issues

• Blocks #15334 (closed)
• Blocks #15706 (closed)
• Blocks #15801 (closed)
• Blocks #15805 (closed)

Original created by @intrigeri on 15803 (Redmine)