CI: fix alma targets

[apostasie]

• [ ] ensure alma test are ran against the right version of containerd, ubuntu and rootlesskit inside the container testing matrix clarified separately
• [ ] figure out why ipfs is currently broken PEBKAC
• enable caching to speed-up the test-integration build
• workaround the losetup weirdness with an extra mount for dev (that sounds vaguely familiar? some old centos / docker issue?) - presumably docker is faulty here against that (old) kernel - and there is a timing issue with how /dev is exposed, causing losetup to fail in a flaky way
• split flaky/not flaky like for the others so we speed-up the run a bit
• migrated TestRunDevice
• non-flaky test suite is passing for both rootless and rootful
• flaky test suite is passing for both rootless and rootful
• [ ] TestStats has no reason to run on cgroups v1 (this is why it is hanging) - investigating to figure out why it would run unclear why it would have hung - might be a side-effect of mounting /dev that fixed it

Currently on top of trivial #3970 (< merge first).

[apostasie]

Ok, CI is green.

I am not 100% confident that I got all of it, but it is an improvement.

Runs are still quite slow (I guess the cost of the extra vm).

Suggesting we merge this and patch more if/when issues crop up.

[AkihiroSuda]

Thanks