extra prompts when logging in using macaroons for HA controllers

[Ian Booth]

When logging in using macaroons and HA controllers, the user is asked to type their password every time a different controller is selected by the juju CLI. This is because the macaroon is stored in a local cookie jar and the cookie url is set to the controller ip address.

Each controller in a HA set up can accept macaroons minted by any of the controllers, as they all share the same bakery key. So the user should only be prompted the first time for their password, and the macaroon stored in the cookie jar such that it can be used for any of the controllers.