Catch exception on addon.register

Exceptions are handled by the common.execute_with_authenticated_user.
If you add type in wrong email and password you are asked again, but
the request is send to /token, which is wrong. By catching the exception
and exiting this is solved.
Merge pull request #36 from cloudControl/registeraddonexception

Catch exception on addon.register
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.