Fix wwctl upgrade nodes to handle kernel argument lists

`wwctl upgrade nodes` could convert legacy kernel argument formats to
the new list format, but then wasn't properly parsing the new list
format for repeat runs.

Signed-off-by: Jonathon Anderson <janderson@ciq.com>

internal/pkg/upgrade/node.go

@@ -588,8 +588,15 @@ type KernelConf struct {
 func (legacy *KernelConf) Upgrade(imageName string) (upgraded *node.KernelConf) {
 	upgraded = new(node.KernelConf)
 	switch args := legacy.Args.(type) {
-	case []string:
-		upgraded.Args = args
+	case []interface{}:
+		for _, arg := range args {
+			switch arg.(type) {
+			case map[string]interface{}, []interface{}, map[interface{}]interface{}:
+				wwlog.Warn("unable to parse Kernel.Args: non-scalar value %v", arg)
+			default:
+				upgraded.Args = append(upgraded.Args, fmt.Sprintf("%v", arg))
+			}
+		}
 	case string:
 		if args != "" {
 			upgraded.Args = strings.Fields(args)

internal/pkg/upgrade/node_test.go

@@ -251,6 +251,74 @@ nodes:
       version: "2.6"
       args:
       - quiet
+`,
+	},
+	{
+		name:            "Kernel args as string",
+		addDefaults:     false,
+		replaceOverlays: false,
+		legacyYaml: `
+nodeprofiles:
+  default:
+    kernel:
+      version: "2.6"
+      args: quiet
+nodes:
+  n1:
+    kernel:
+      version: "2.6"
+      args: quiet
+`,
+		upgradedYaml: `
+nodeprofiles:
+  default:
+    kernel:
+      version: "2.6"
+      args:
+      - quiet
+nodes:
+  n1:
+    kernel:
+      version: "2.6"
+      args:
+      - quiet
+`,
+	},
+	{
+		name:            "Kernel args as list",
+		addDefaults:     false,
+		replaceOverlays: false,
+		legacyYaml: `
+nodeprofiles:
+  default:
+    kernel:
+      version: "2.6"
+      args:
+      - quiet
+      - 1
+nodes:
+  n1:
+    kernel:
+      version: "2.6"
+      args:
+      - quiet
+      - 2
+`,
+		upgradedYaml: `
+nodeprofiles:
+  default:
+    kernel:
+      version: "2.6"
+      args:
+      - quiet
+      - "1"
+nodes:
+  n1:
+    kernel:
+      version: "2.6"
+      args:
+      - quiet
+      - "2"
 `,
 	},
 	{