[WIP] archive: LCOW refactor (rebased)

[thaJeztah]

rebase of #39386, relates to #39533. Just rebased to see where/how this failed, as CI logs were gone

Big refactor with containerfs to remove duplicate code from LCOW
Deletes lot of dead code in the process.

TODO: fix tests that relied on those functions/types.

[AkihiroSuda]

relates to #39533.

What's the goal of this PR? IIUC we are going to remove LCOW codes after this refactoring?

[thaJeztah]

I was mostly curious how much work was left to get this finished, as it removed quite some code (so less to maintain?). As to removing LCOW; that mostly depends on how much bandwidth we have to work on that. I opened #40766 some time back to allow disabling the functionality, after which if could be possible to start working on removing it.

ISTR there were still some uses of LCOW by Microsoft, but if they want the functionality to remain, I guess some help would be needed to maintain the code.

[thaJeztah]

These are the failures;

[2020-07-29T14:21:29.522Z] WARN [runner] Can't run linter unused: buildssa: analysis skipped: errors in package:

/go/src/github.com/docker/docker/integration/plugin/authz/authz_plugin_test.go:397:26: CopyInfoSourcePath not declared by package archive
/go/src/github.com/docker/docker/integration/plugin/authz/authz_plugin_test.go:399:29: TarResource not declared by package archive
/go/src/github.com/docker/docker/integration/plugin/authz/authz_plugin_test.go:403:42: PrepareArchiveCopy not declared by package archive
/go/src/github.com/docker/docker/integration/plugin/authz/authz_plugin_test.go:403:90: CopyInfo not declared by package archive]

[2020-07-29T14:25:47.506Z] === Failed
[2020-07-29T14:25:47.506Z] === FAIL: pkg/chrootarchive TestChrootTarUntarWithSymlink (0.36s)
[2020-07-29T14:25:47.506Z] panic: runtime error: invalid memory address or nil pointer dereference [recovered]
[2020-07-29T14:25:47.506Z] 	panic: runtime error: invalid memory address or nil pointer dereference
[2020-07-29T14:25:47.506Z] [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x239484]
[2020-07-29T14:25:47.506Z]
[2020-07-29T14:25:47.506Z] goroutine 22 [running]:
[2020-07-29T14:25:47.506Z] testing.tRunner.func1(0xc0000a4500)
[2020-07-29T14:25:47.506Z] 	/usr/local/go/src/testing/testing.go:874 +0x41a
[2020-07-29T14:25:47.506Z] panic(0x30dc40, 0x5b6140)
[2020-07-29T14:25:47.506Z] 	/usr/local/go/src/runtime/panic.go:679 +0x1d4
[2020-07-29T14:25:47.506Z] github.com/docker/docker/pkg/archive.(*Archiver).TarUntar(0xc00005a380, 0xc000018380, 0x36, 0xc000018a40, 0x37, 0x0, 0x0)
[2020-07-29T14:25:47.506Z] 	/go/src/github.com/docker/docker/pkg/archive/archive.go:1085 +0x104
[2020-07-29T14:25:47.506Z] github.com/docker/docker/pkg/chrootarchive.TarUntar(...)
[2020-07-29T14:25:47.506Z] 	/go/src/github.com/docker/docker/pkg/chrootarchive/archive_test.go:29
[2020-07-29T14:25:47.506Z] github.com/docker/docker/pkg/chrootarchive.TestChrootTarUntarWithSymlink(0xc0000a4500)
[2020-07-29T14:25:47.506Z] 	/go/src/github.com/docker/docker/pkg/chrootarchive/archive_test.go:192 +0x3ce
[2020-07-29T14:25:47.506Z] testing.tRunner(0xc0000a4500, 0x379488)
[2020-07-29T14:25:47.506Z] 	/usr/local/go/src/testing/testing.go:909 +0xd6
[2020-07-29T14:25:47.506Z] created by testing.(*T).Run
[2020-07-29T14:25:47.506Z] 	/usr/local/go/src/testing/testing.go:960 +0x36c
[2020-07-29T14:25:47.506Z] FAIL	github.com/docker/docker/pkg/chrootarchive	0.363s
[2020-07-29T14:25:47.506Z]
[2020-07-29T14:25:47.506Z]
[2020-07-29T14:25:47.506Z] === Errors
[2020-07-29T14:25:47.506Z] pkg/archive/archive_test.go:36:5: defaultArchiver redeclared in this block
[2020-07-29T14:25:47.506Z] 	previous declaration at pkg/archive/archive.go:78
[2020-07-29T14:25:47.506Z] pkg/archive/archive_unix_test.go:125:15: undefined: TarResourceRebase
[2020-07-29T14:25:47.506Z] pkg/archive/archive_unix_test.go:130:13: undefined: RebaseArchiveEntries
[2020-07-29T14:25:47.506Z] pkg/archive/archive_unix_test.go:264:12: undefined: CopyInfo