debian,vendor: import github.com/snapcore/squashfs and use

[mvo5]

This PR will add a new vendor dependency github.com/snapcore/squashfs
that is used to provide squashfuse for lxd.

It superseeds #4030 and still needs some love but for early review it should be ok. Some trickery needed to make github.com/snapcore/squashfuse go get able (snapcore/squashfuse@ed6f37b).

[Conan-Kudo]

@mvo5 This is a bit less gross, but why do this through the go vendor?

[pedronis]

marked as blocked as apparently it's not fully working and we need to look into a different approach according to @mvo5

[mvo5]

This needs a forum topic with "upcoming" tag and then can be closed.

[zyga]

@mvo5 shall we close this or do you think it is a viable approach but just needs more work?

[Conan-Kudo]

Please don't do it this way. If you must vendor it, do it the more standard way (add an additional tarball to the dsc packaging and build it appropriately).

Shoehorning into weird Go things is just horrible.

[codecov-io]

Codecov Report

Merging #4049 into master will decrease coverage by <.01%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master    #4049      +/-   ##
==========================================
- Coverage   78.04%   78.03%   -0.01%     
==========================================
  Files         449      449              
  Lines       30907    30912       +5     
==========================================
+ Hits        24121    24122       +1     
- Misses       4774     4779       +5     
+ Partials     2012     2011       -1

Impacted Files	Coverage Δ
systemd/systemd.go	83.98% <50%> (-0.6%)	⬇️
overlord/ifacestate/helpers.go	63.48% <0%> (-0.83%)	⬇️

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[mvo5]

@Conan-Kudo Yes, sorry for this. Unfortunately there is no clean deb package way to vendor this, this hack is about the cleanest solution I was able to find :/

[Conan-Kudo]

@mvo5 Last I checked, you should be able to just attach more source tarballs in the dsc description when uploading to Ubuntu. The rules file can be adjusted to actually use the second source vendor it in. In addition, this change should be considered temporary and dropped for bionic, as that release can just use regular squashfuse. Same goes for Debian sid.

There's no good reason to make a permanent hack here.