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

To soften the dependency on log.Entry and to separate the functionality
from CLI code. This also makes code easier to move around and avoids
hiding function complexity.

Part of #630

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

cli/cmd/component-render-manifest.go

@@ -40,19 +40,28 @@ 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 := selectComponentNames(args, *lokoConfig.RootConfig)
+	componentsToRender := selectComponentNames(componentsList, *lokoConfig.RootConfig)
 
 	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 {