main: unif/refactor std{out,err} test handling

[lzap]

For historic reasons we have two way to test the std{out,err} output. One is to just monkey patch var osStdout = os.Stdout and then replace it in the tests, the other to have a helper that works like a with in python that replaces the stdout/stderr dynamically, e.g.:

stdout, stderr := testutil.CaptureStdio(t, func() {
 err = main.Run()
 require.NoError(t, err)
})

The trouble is that they are not quite compatible. In places where we use the monkey patches osStdout the
testutil.CaptureStdio() will not work as it (temporarely) replaces the "real" os.Stdout (and vice-versa).

So this commit unifies all tests to use testutil.CaptureStdio() which feels slightly nicer than the other approach in the sense that one does not need to remember to use osStdout in the code. Its mostly mechanical.

---

I rebased #416 on top of main, review carefully thanks :)

[lzap]

TestManifestIntegrationSmoke fails, need to take a look.

[lzap]

Rebased, fixed the test, it seems unrelated so something wrong was merged?

I do not think it is worth implementing any complex JSON testing for these smoke tests, at least for now.

[supakeen]

Needs a rebase.

[lzap]

Done.

[supakeen]

Thank you :)

[lzap]

Weird, all passes locally but on CICD:

=== RUN   TestManifestIntegrationOstreeSmoke
    main_test.go:271: 
        	Error Trace:	/__w/image-builder-cli/image-builder-cli/cmd/image-builder/main_test.go:271
        	Error:      	
        	Test:       	TestManifestIntegrationOstreeSmoke
--- FAIL: TestManifestIntegrationOstreeSmoke (6.20s)

Ha this must be a different osbuild version that I have vs what is in here. The failing line is:

assert.Contains(t, stdout, `{"type":"org.osbuild.ostree.init-fs"`)

Smoke tests run in Fedora 43.

[lzap]

I had to add t.Log to see the damn stdout. Ignore the --amend commit message that was a typo and will go anyway :-)

[lzap]

Oh wait I think I fixed the issue by the previous commit already but there is a different one:

 where 2 = CompletedProcess(args=['podman', 'run', '--rm', '--privileged', '--security-opt', 'label=type:unconfined_t', '-v', '/var/lib/containers/storage:/var/lib/containers/storage', '-v', '/mnt/var/tmp/bib-tests/test_opts_arch_is_same_arch_is1/output:/output', 'bootc-image-builder-test-faked-osbuild', '--type=iso', 'quay.io/centos-bootc/centos-bootc:stream9', '--target-arch=amd64'], returncode=2, stdout='', stderr="Generating manifest manifest-iso.json\nManifest generation step\nerror invalid request\nInvalidRequest: No 'repos' or 'root_dir' specified\npanic: runtime error: index out of range [0] with length 0\n\ngoroutine 1 [running]:\ngithub.com/osbuild/images/pkg/manifest.(*AnacondaInstaller).serialize(0xc0007b1508)\n\t/root/go/pkg/mod/github.com/osbuild/images@v0.244.0/pkg/manifest/anaconda_installer.go:311 +0x10bc\ngithub.com/osbuild/images/pkg/manifest.Manifest.Serialize({{0xc000f8ed00, 0x5, 0x8}, 0x2, {0x0, 0x0}}, 0x0, 0xc0007df8c0, 0xc00076e9f0, 0xc00085d300)\n\t/root/go/pkg/mod/github.com/osbuild/images@v0.244.0/pkg/manifest/manifest.go:208 +0x3fd\ngithub.com/osbuild/images/pkg/manifestgen.(*Generator).Generate(0xc000c12360, 0xc000640820, {0x3b6dd30, 0xc00097b208}, 0x4?)\n\t/root/go/pkg/mod/github.com/osbuild/images@v0.244.0/pkg/manifestgen/manifestgen.go:230 +0xb55\nmain.bibManifestFromCobra(0xc000254f08, {0xc000497320, 0x1, 0xc0005a0650?}, {0x3b63430, 0xc0005a0630})\n\t/build/cmd/image-builder/bib_main.go:213 +0xd0e\nmain.bibCmdBuild(0xc000254f08, {0xc000497320, 0x1, 0x3})\n\t/build/cmd/image-builder/bib_main.go:335 +0x7fb\ngithub.com/spf13/cobra.(*Command).execute(0xc000254f08, {0xc000497260, 0x3, 0x3})\n\t/root/go/pkg/mod/github.com/spf13/cobra@v1.10.2/command.go:1015 +0xb02\ngithub.com/spf13/cobra.(*Command).ExecuteC(0xc000254908)\n\t/root/go/pkg/mod/github.com/spf13/cobra@v1.10.2/command.go:1148 +0x465\ngithub.com/spf13/cobra.(*Command).Execute(...)\n\t/root/go/pkg/mod/github.com/spf13/cobra@v1.10.2/command.go:1071\nmain.bibRun()\n\t/build/cmd/image-builder/bib_main.go:605 +0x29\nmain.main()\n\t/build/cmd/image-builder/main.go:689 +0x5a\n").returncode

[lzap]

osbuild/images#2243

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