engine: resources: Add missing WatchCmd UID

Not sure if this is even used anywhere, but might as well add it for
now.

engine/resources/exec.go

@@ -592,6 +592,7 @@ func (obj *ExecRes) Interrupt() error {
 type ExecUID struct {
 	engine.BaseUID
 	Cmd      string
+	WatchCmd string
 	IfCmd    string
 	// TODO: add more elements here
 }
@@ -680,6 +681,7 @@ func (obj *ExecRes) UIDs() []engine.ResUID {
 	x := &ExecUID{
 		BaseUID:  engine.BaseUID{Name: obj.Name(), Kind: obj.Kind()},
 		Cmd:      obj.getCmd(),
+		WatchCmd: obj.WatchCmd,
 		IfCmd:    obj.IfCmd,
 		// TODO: add more params here
 	}