Registry Notification Mails

[georgschermann]

Since we have a lot of hosts in the registry we get a lot of notifications with a lot of false positives and a lot of 1-3 Minute downs. These several hundred mails a day don't really fit the purpose.
I'd suggest that the registry tries to re-fetch a manifest after some time after a connection error or waits for a 2nd failed fetch before sending notification mails or something similar. If this is not possible we will have to remove the admin-emails.