Change juju gui password to 'admin' causes --show-credentials to show blank password

[Mark W Wenning]

To duplicate:
1. Install juju 2.0 rc2
2. Change 'admin' password to 'admin' instead of the randomly generated UID
3. Bootstrap juju
4. Run 'juju gui --show credentials'
5. Credentials will show up as login = admin@local, password=

i.e. blank password. admin/admin will still work on the juju gui screen, but the cli command will not list any password.

[Francesco Banconi (frankban)]

This also affects "juju show-controller --show-password": the password is no longer included in the output after changing the initial one.

[Anastasia (anastasia-macmood)]

I'll look into this but it's possible that the password will not be available once changed since we are keeping it in an encrypted form and the way security works, I imagine, is that we cannot decrypt it.

Either way, since this report was filed, the output of juju GUI after a password change, shows:

```
$ juju gui --show-credentials
GUI 2.14.0 for model "admin/default" is enabled at:
  https://[redacted]/gui/u/admin/default
Your login credential is:
  username: admin
  password: <unknown> (password has been changed by the user)

```

But the 'show-controller --show-password' is still omitted when password is changed for the 'admin' user.

[Anastasia (anastasia-macmood)]

So prior to using macaroons, we used to store passwords on client's disk. With macaroons, we have explicitly opted not to store the password but store macaroon instead. This means that all commands that relied on this information being stored on disk, stopped working.

[Anastasia (anastasia-macmood)]

Actually this is a duplicate of another bug where is a better discussion around 'why we should [i.e. should not] expose/store plain text password?'