Fix: prioritize namespace flag for vela up

Currently, CLI applies application to `default` namespace when there is
no explicit namespace in application spec, even if the namespace flag
is set.

This commit fixes issue by overriding the namespace if the namespace
flag is set.

Signed-off-by: Sunghoon Kang <hoon@linecorp.com>

references/cli/up.go

@@ -68,6 +68,10 @@ func NewUpCommand(c common2.Args, order string, ioStream cmdutil.IOStreams) *cob
 			if err != nil {
 				return errors.Wrap(err, "File format is illegal, only support vela appfile format or OAM Application object yaml")
 			}
+			// override namespace if namespace flag is set
+			if namespace != "" {
+				app.SetNamespace(namespace)
+			}
 			err = common.ApplyApplication(app, ioStream, kubecli)
 			if err != nil {
 				return err