Unify command line namespace resolution

This change allows the namespace in kubeconfig to be overridden by
specifying the namespace in the spec file. If namespace is explicitly
provided in the command line flags and the spec file has a different
namespace, this will cause an error.

pkg/kubectl/cmd/create.go

@@ -75,7 +75,7 @@ func RunCreate(f *cmdutil.Factory, out io.Writer, filenames util.StringList) err
 		return err
 	}
 
-	cmdNamespace, err := f.DefaultNamespace()
+	cmdNamespace, enforceNamespace, err := f.DefaultNamespace()
 	if err != nil {
 		return err
 	}
@@ -84,8 +84,8 @@ func RunCreate(f *cmdutil.Factory, out io.Writer, filenames util.StringList) err
 	r := resource.NewBuilder(mapper, typer, f.ClientMapperForCommand()).
 		Schema(schema).
 		ContinueOnError().
-		NamespaceParam(cmdNamespace).RequireNamespace().
-		FilenameParam(filenames...).
+		NamespaceParam(cmdNamespace).DefaultNamespace().
+		FilenameParam(enforceNamespace, filenames...).
 		Flatten().
 		Do()
 	err = r.Err()