cli/cmd: make component render-manifest use errors instead of Fatalf

To remove a dependency on log.Entry to make moving this code around
easier and to avoid hiding function complexity from logger.

Part of #630

Signed-off-by: Mateusz Gozdek <mateusz@kinvolk.io>

cli/cmd/component-render-manifest.go

@@ -40,19 +40,35 @@ func runComponentRender(cmd *cobra.Command, args []string) {
 		"args":    args,
 	})
 
+	if err := componentRenderManifest(contextLogger, args); err != nil {
+		contextLogger.Fatalf("Rendering component manifests failed: %v", err)
+	}
+}
+
+func componentRenderManifest(contextLogger *log.Entry, componentsList []string) error {
 	lokoConfig, diags := getLokoConfig()
 	if diags.HasErrors() {
 		for _, diagnostic := range diags {
 			contextLogger.Error(diagnostic.Error())
 		}
-		contextLogger.Fatal("Errors found while loading configuration")
+
+		return diags
 	}
 
-	componentsToRender := componentNames(args, *lokoConfig)
+	var componentsToRender []string
+	if len(componentsList) > 0 {
+		componentsToRender = append(componentsToRender, componentsList...)
+	} else {
+		for _, component := range lokoConfig.RootConfig.Components {
+			componentsToRender = append(componentsToRender, component.Name)
+		}
+	}
 
 	if err := renderComponentManifests(lokoConfig, componentsToRender); err != nil {
-		contextLogger.Fatal(err)
+		return fmt.Errorf("rendering component manifests: %w", err)
 	}
+
+	return nil
 }
 
 func renderComponentManifests(lokoConfig *config.Config, componentNames []string) error {