removed (sometimes) confusing error message (bnc#889531)

Whether the email or the reg code was invalid is specified in the details,
the reason for not registering might be something else than invalid user
input. The error message can be confusing in some situations.
reset registration status on failure (bnc#889531)

to register from scratch and avoid half-registered system
(makes troubles when retrying registration with another
registration server)
changes

- 3.1.101
Merge pull request #143 from yast/error_reporting

Better error handling