unit: refactor config

- Seperate the config from Destination()
- Add YAML tags for the fields

config/unit.go

@@ -0,0 +1,34 @@
+package config
+
+import (
+	"path/filepath"
+	"strings"
+)
+
+type Unit struct {
+	Name    string `yaml:"name"`
+	Mask    bool   `yaml:"mask"`
+	Enable  bool   `yaml:"enable"`
+	Runtime bool   `yaml:"runtime"`
+	Content string `yaml:"content"`
+	Command string `yaml:"command"`
+
+	// For drop-in units, a cloudinit.conf is generated.
+	// This is currently unbound in YAML (and hence unsettable in cloud-config files)
+	// until the correct behaviour for multiple drop-in units is determined.
+	DropIn bool `yaml:"-"`
+}
+
+func (u *Unit) Type() string {
+	ext := filepath.Ext(u.Name)
+	return strings.TrimLeft(ext, ".")
+}
+
+func (u *Unit) Group() string {
+	switch u.Type() {
+	case "network", "netdev", "link":
+		return "network"
+	default:
+		return "system"
+	}
+}