log successful connections too

So we can use that to prioritize successful connections for known domains (Gmail, Google Apps, Yahoo etc). Some of my successful connections:

* ownCloud.com: imap.owncloud.com, 143, (plain username before @), tls
* Google Apps: imap.gmail.com, 993, (full email address), ssl
* iCloud: **imap.mail.me.com**, 993, (plain username before @), ssl (didn’t [just as in the docs](http://support.apple.com/kb/HT4864))

ownCloud and Google Apps worked through autodiscovery, but iCloud not because it still has the weird mail.me.com imap address.

cc @DeepDiver1975