Make the login prompt configurable

The different platforms use different kind of logins:
 - cloudcontrolled uses 'Email'
 - dotcloudapp uses 'Email'
 - app.exo.io uses 'Email or Organization ID'
 - cnh-apps uses 'Login'

Especially on cloud&heat the login is a combination of tenant_name
and email. Asking only for the email confuses the customers (and me).
Merge pull request #35 from cloudControl/differentlogin

Make the login prompt configurable
Prompt for updating right package when old version

Fixes #33

Previously this was hardcoded, so the user always go a message to upgrade
`cctrl` regardless of which package where they using.

This still checks the version of `cctrl` package, but ideally this
should equal the ones from dotcloudng, cnh or another clones.