The scaleup subcommand does not support the unattended option

* 'atomic-openshift-installer' will exit now if -u is given with the
  'scaleup' subcommand
* https://bugzilla.redhat.com/show_bug.cgi?id=1390135

utils/src/ooinstall/cli_installer.py

@@ -1124,6 +1124,20 @@ def scaleup(ctx, gen_inventory):
 
     click.echo('Welcome to the OpenShift Enterprise 3 Scaleup utility.')
 
+    # Scaleup requires manual data entry. Therefore, we do not support
+    # unattended operations.
+    if unattended:
+        msg = """
+---
+
+The 'scaleup' operation does not support unattended
+functionality. Re-run the installer without the '-u' or '--unattended'
+option to continue.
+"""
+        click.echo(msg)
+        sys.exit(1)
+
+    # Resume normal scaleup workflow
     print_installation_summary(installed_hosts,
                                oo_cfg.settings['variant_version'],
                                verbose=False,)