Always prompt for a password when asking for credentials.

There is a weird behavior where we don't ask for a password
when the user you type in the prompt is the same you have configured
in the config file.

This is the source of many frustrations and also a bug.
If the authentication with a registry fails because the password
is incorrect, we won't ask for the password again with the current logic.

With this change, we also stop calling `CmdLogin` directly when
authentication fails. We don't need to parse flags from the cli or
setting up input destriptiors again, like the current behavior is doing.

Signed-off-by: David Calavera <david.calavera@gmail.com>