Handle case from JENKINS-16332

Added ability to handle case where we get full name with email like "Firstname Lastname _username@domain.com_", currently MailAddressResolver takes the following path:

```
 if(u.getFullName().contains("@"))
            // this already looks like an e-mail ID
            return u.getFullName();
```

Which results in an invalid email address that is just the same "Firstname Lastname _username@domain.com_".

Added code to extractAddressFromId to check for this case and return the correct email address.

Added two tests that verify the new code works.