The Add credential button on the Ansible Tower configuration section does not work when adding new items.

Steps to reproduce:

1. Go to the global Jenkins configuration page
2. On the Ansible Tower section, click on Add to start adding a new Ansible Tower installation
3. On the credentials field, click on the Add button, nothing happens.

Expected result:

It should show a list of credentials provider when the Add credential button is pressed and allow creating a new credential.

Additional details:

If you add a Tower Installation and try to click on the Add button for its credentials field it works as expected.