Add a helper function in usd/git_repository to extract the distribution
target from d/changelog and use that value and the version to generate
standard tag messages.
If we actually failed permanently to download a file, we wouldn't see
it, because we only iterate self.retries times, and the iterated value
goes up to self.retries-1. So we never end up triggering the condition.
We have seen network stalls and connection issues when we use a
long-lived launchpad connection. Instead, re-establish the connection on
each main loop iteration.
