isobuilders are getting stuck

Originally created by @anonym on #11350 (Redmine)

At the moment, all builds are on over 2h build time. They all get stuck on fetching the Tor Browser tarballs. One isobuilder managed to fetch two tarballs, and then getting stuck on the third, while the others are stuck on the first tarball. Either it’s related to that, or something crazy happened around 16:56:08 on all isobuilders (or on the host?), because that is the last timestamp in all their Console Output logs.

Currently, these are the stuck jobs:

• isobuilder1:
  https://jenkins.tails.boum.org/job/build_Tails_ISO_bugfix-10866-otr-bot-vs-unicode/1/
• isobuilder2:
  https://jenkins.tails.boum.org/job/build_Tails_ISO_web-11269-download-only/25/
• isobuilder3:
  https://jenkins.tails.boum.org/job/build_Tails_ISO_doc-10179-mentors/31/
• isobuilder 4:
  https://jenkins.tails.boum.org/job/build_Tails_ISO_test-10721-a11y-technologies/10/