Try 3 times before failing to talk to pkgdb2.

This should hopefully cut down on the fedmsg error mails.  Almost all of them
these days are from the connection to pkgdb2 failing for some reason (once an
hour-ish?).
Merge pull request #12 from fedora-infra/feature/careful-with-the-pkgdb2-plz

Try 3 times before failing to talk to pkgdb2.