Fix dashboard not found error msg

[barrettj12]

The juju dashboard command was displaying an unfriendly error when the dashboard was not deployed/available:

$ juju dashboard
ERROR getting dashboard address for controller "foo": dashboard address in relation data not found

The error returned from the API client was not being converted to a juju/errors error. We just need to use the params.TranslateWellKnownError function to convert this to an error that we can pattern match against.

QA steps

$ juju bootstrap lxd c
$ juju dashboard
The Juju dashboard is not yet deployed.
To deploy the Juju dashboard, follow these steps:
  juju switch controller
  juju deploy juju-dashboard
  juju expose juju-dashboard
  juju relate juju-dashboard controller

Bug reference

https://bugs.launchpad.net/juju/+bug/1994953

[barrettj12]

/merge

[barrettj12]

/merge