FR-6365 - Improve mountpoints handling

[upils]

Notable changes in this PR:

• when executing some commands needing to mount some mountpoints in the chroot:
  • unmounting and "teardown" commands are now only executed in defer statements
  • if these commands fail, they do not prevent others from running. The goal is to hopefully unmount as many mountpoints as possible is something is going wrong. Letting some mountpoint behind is not ideal but should not prevent the image building from completing.
• run udevadm settle before tearing down mount points after package installation to hopefully make it more reliable
• replace bind mounts where possible. Instead directly mount /proc and such.
• specify the mount type to make sure mountpoints are correctly handled.
• be more granular on /dev mounting.

Solves LP: #2049695

[codecov]

Codecov Report

Attention: 12 lines in your changes are missing coverage. Please review.

Comparison is base (2e283da) 90.05% compared to head (e09205b) 79.50%.

Files	Patch %	Lines
internal/statemachine/classic_states.go	92.94%	5 Missing and 1 partial ⚠️
internal/statemachine/helper.go	91.89%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #178       +/-   ##
===========================================
- Coverage   90.05%   79.50%   -10.55%     
===========================================
  Files          13       13               
  Lines        3430     3504       +74     
===========================================
- Hits         3089     2786      -303     
- Misses        304      671      +367     
- Partials       37       47       +10     

Flag	Coverage Δ
unittests	79.50% <92.45%> (-10.55%)	⬇️

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[mwhudson]

This is probably fine. I think the commit message is a both a bit vague and a bit optimistic though? Something like "run udevadm settle before tearing down mount points after package installation to hopefully make it more reliable" or something would be better to me...

[upils]

Oh do not worry about the commit's messages for now, I am still investigating and will write proper commits when I have pinpointed the solution.

[sil2100]

Looks good. The inline comments are non-important pokes.
Makes me actually think why we did bind-mount so many of the mountpoints to begin with. Must have been something I missed during reviews, since we don't even do that in livecd-rootfs. Anyway, this looks like the right way forward. Please proceed!

[sil2100]

Oh, and don't forget to bump snapcraft.yaml! So that at least the edge snap gets a +snapX bump.

[upils]

Oh, and don't forget to bump snapcraft.yaml! So that at least the edge snap gets a +snapX bump.

Yes. I tend to do that just before merging because we already had several occasions where I needed to change it a few times because several other PR where merged just before merging the one I was working on.