list-roles should print to stdout and not stderr

[grosser]

2.22.1 printed the list of accounts to stdout, which allowed to pipe it to a file and still show the user some output
2.27.0 writes everything to stderr, so now I cannot separate them easily and things like Success. Logging you in... ends up in the output

please make the output go to stdout again

[LorisCazalon]

hello, as a workaround in our scripts that get saml2aws, i propose to also get the content of the stderr : https://github.com/zendesk/dotfiles_n_scripts/pull/81.
We should revert the PR once this is fixed

[grosser]

Bug was added in #502