MCO-708: Extract and merge kernel arguments from /proc/cmdline

In firstboot MCO checks if reboot can be skipped.  In order for reboot
to be skipped, the kernel arguments of the current (booted) system and
the expected system need to match.
Currently, in firstboot the list of the current kargs is assumed to be
empty.  To reflect the actual list of arguments the system was booted
with, this change extracts the set of booted kargs from /proc/cmdline
to be used for comparison.
Only kargs that appear both in the requested kargs and /proc/cmdline are used for comparison.

pkg/daemon/daemon.go

@@ -1054,6 +1054,10 @@ func (dn *Daemon) RunFirstbootCompleteMachineconfig() error {
 	// it, reflecting the current machine state.
 	oldConfig := canonicalizeEmptyMC(nil)
 	oldConfig.Spec.OSImageURL = dn.bootedOSImageURL
+	if err = mergeRunningKargs(oldConfig, mc.Spec.KernelArguments); err != nil {
+		return fmt.Errorf("failed to merge kernel arguments: %w", err)
+	}
+
 	// Currently, we generally expect the bootimage to be older, but in the special
 	// case of having bootimage == machine-os-content, and no kernel arguments
 	// specified, then we don't need to do anything here.

pkg/daemon/update.go

@@ -122,6 +122,24 @@ func (dn *Daemon) performPostConfigChangeAction(postConfigChangeActions []string
 	return dn.triggerUpdateWithMachineConfig(state.currentConfig, state.desiredConfig, true)
 }
 
+func mergeRunningKargs(config *mcfgv1.MachineConfig, requestedKargs []string) error {
+	b, err := os.ReadFile("/proc/cmdline")
+	if err != nil {
+		return err
+	}
+	splits := strings.Split(strings.TrimSpace(string(b)), " ")
+	for _, split := range splits {
+		for _, reqKarg := range requestedKargs {
+			if strings.ReplaceAll(reqKarg, "\"", "") == strings.ReplaceAll(split, "\"", "") {
+				config.Spec.KernelArguments = append(config.Spec.KernelArguments, reqKarg)
+				break
+			}
+		}
+	}
+	logSystem("requested kargs: %+v, merged kargs: %+v", requestedKargs, config.Spec.KernelArguments)
+	return nil
+}
+
 func canonicalizeEmptyMC(config *mcfgv1.MachineConfig) *mcfgv1.MachineConfig {
 	if config != nil {
 		return config