mantle/platform: make copied ISO file writable for tests

Since we are going to modify it let's ensure it's writable.

We are changing up some of the code that builds the Live artifacts
and it exposed the fact that we are relying here on the files in
the builddir to have the writable bit set. Let's not rely on that.

Author: dustymabe

mantle/platform/metal.go

@@ -668,6 +668,10 @@ func (inst *Install) InstallViaISOEmbed(kargs []string, liveIgnition, targetIgni
 	if err := cmd.Run(); err != nil {
 		return nil, errors.Wrapf(err, "copying iso")
 	}
+	// Make it writable so we can modify it
+	if err := os.Chmod(newIso, 0644); err != nil {
+		return nil, errors.Wrapf(err, "setting permissions on iso")
+	}
 	srcisopath = newIso
 
 	var metalimg string

mantle/platform/qemu.go

@@ -1500,6 +1500,10 @@ func (builder *QemuBuilder) setupIso() error {
 	if err := cpcmd.Run(); err != nil {
 		return errors.Wrapf(err, "copying iso")
 	}
+	// Make it writable so we can modify it
+	if err := os.Chmod(isoEmbeddedPath, 0644); err != nil {
+		return errors.Wrapf(err, "setting permissions on iso")
+	}
 	if builder.ConfigFile != "" {
 		if builder.configInjected {
 			panic("config already injected?")