`maas login` tells you you're logged in successfully when you're not

[Graham Binns]

Passing nonsense credentials to `maas login` gives you a "success" message:

graham@dorfl: maas$ maas login foobar http://maas-master.marybank.local/MAAS thisis:all:nonsense

You are now logged in to the MAAS server at http://maas-
master.marybank.local/MAAS/api/1.0/ with the profile name 'foobar'.

For help with the available commands, try:

  maas foobar --help

graham@dorfl: maas$ maas foobar node-groups list
Invalid consumer.