add bash completion for abra cmd

pkg/autocomplete/autocomplete.go

@@ -25,6 +25,16 @@ func AppNameComplete(c *cli.Context) {
 	}
 }
 
+func ServiceNameComplete(appName string) {
+	serviceNames, err := config.GetAppServiceNames(appName)
+	if err != nil {
+		return
+	}
+	for _, s := range serviceNames {
+		fmt.Println(s)
+	}
+}
+
 // RecipeNameComplete completes recipe names.
 func RecipeNameComplete(c *cli.Context) {
 	catl, err := recipe.ReadRecipeCatalogue(false)