View-related (and other minor) changes to !5951 based on @rymai's review.

- The `scopes_form` partial can be used in the `admin/applications` view
  as well

- Don't allow partials to access instance variables directly. Instead, pass
  in the instance variables as local variables, and use `local_assigns.fetch`
  to assert that the variables are passed in as expected.

- Change a few instances of `render :partial` to `render`

- Remove an instance of `required: false` in a view, since this is the default

- Inline many instances of a local variable (`ip = 'ip'`) in `auth_spec`