Snap builds often failing on proxy errors

[Sebastien Bacher]

We have been struggling with some of our desktop snap build recently due them often hitting proxy errors

One example from today (which might vanish from the library because the build got retried)
https://launchpadlibrarian.net/694069284/buildlog_snap_ubuntu_jammy_amd64_firefox-snap-nightly_BUILDING.txt.gz

```
:: + wget https://ftp.mozilla.org/pub/firefox/nightly/latest-mozilla-central-l10n/linux-x86_64/xpi/firefox-121.0a1.sv-SE.langpack.xpi
:: --2023-10-25 13:15:22-- https://ftp.mozilla.org/pub/firefox/nightly/latest-mozilla-central-l10n/linux-x86_64/xpi/firefox-121.0a1.sv-SE.langpack.xpi
:: Connecting to 10.10.10.1:8222... connected.
:: Proxy tunneling failed: Proxy Authentication RequiredUnable to establish SSL connection.
'override-pull' in part 'firefox-langpacks' failed with code 4.
Review the scriptlet and make sure it's correct.
Full execution log: '/root/.local/state/snapcraft/log/snapcraft-20231025-130847.733750.log'
Build failed
```

This specific build was on firefox for amd64 but it's also impacting other snaps and architectures

It is quite problematic since it impacts our capacity to get firefox (security) updates for Ubuntu out

[Amin Bandali (bandali)]

Thanks for opening this bug report, Seb.

FWIW I've indeed noticed more of these recently. Though they've always been a thing for Firefox snap ARM builds. Like, I almost always have to retry an armhf or arm64 Firefox snap build at least once each time. I think Nathan has had similar experience for chromium snap builds.

edit: another failure just now: https://launchpadlibrarian.net/694087763/buildlog_snap_ubuntu_jammy_armhf_firefox-snap-beta_BUILDING.txt.gz

[Nathan Teodosio (nteodosio)]

I'm not so lucky to get proxy errors — at least not explicitly explained like that —, I usually get the more enigmatic

--->
Executing parts lifecycle: pull chromium
Executing action
:: + set -eux
:: + craftctl default
None
<---

https://launchpadlibrarian.net/692643685/buildlog_snap_ubuntu_jammy_armhf_chromium-snap-from-source-stable_BUILDING.txt.gz

[William Grant (wgrant)]

This was an IO performance issue on the builder proxy authentication service, that has now been fixed by moving to NVMe.