mantle/kola/testiso: expose testiso debug via COSA_TESTISO_DEBUG env var

This will be useful in the future when trying to debug earlyboot testiso
issues further.

mantle/cmd/kola/testiso.go

@@ -773,6 +773,14 @@ func testLiveIso(ctx context.Context, inst platform.Install, outdir string, mini
 		isoKernelArgs = append(isoKernelArgs, liveISOFromRAMKarg)
 	}
 
+	// Sometimes the logs that stream from various virtio streams can be
+	// incomplete because they depend on services inside the guest.
+	// When you are debugging earlyboot/initramfs issues this can be
+	// problematic. Let's add a hook here to enable more debugging.
+	if _, ok := os.LookupEnv("COSA_TESTISO_DEBUG"); ok {
+		isoKernelArgs = append(isoKernelArgs, "systemd.log_color=0 systemd.log_level=debug systemd.log_target=console")
+	}
+
 	mach, err := inst.InstallViaISOEmbed(isoKernelArgs, liveConfig, targetConfig, outdir, isOffline, minimal)
 	if err != nil {
 		return 0, errors.Wrapf(err, "running iso install")