Right now the worst case chain of events for building an ISO on Hydra is
- copy everything to squashfs builder
- run squashfs builder
- download squashfs from builder
- compress squashfs
- upload squashfs to S3
- copy squashfs to ISO builder
- run ISO builder
- download ISO from builder
- compress ISO
- upload ISO to S3
This inlines the squashfs build into the ISO build, which makes it
- copy everything to ISO builder
- run ISO builder
- download ISO from builder
- compress ISO
- upload ISO to S3
Which should reduce queue runner load by $alot per ISO, which we have four of on small channels
(one release, one test per arch) and a lot more than four of on large channels (with various desktops)