Gracefully handle failure to open urls

[jdswinbank]

The code has a couple of raw calls to urlopen, which might fail (because the resource is offline, for example). When they do, the exception causes us to come crashing out, and I get e-mail.

Should implement some sort of backoff and retry, only sending mail if the error is persistent.

[jdswinbank]

Note the calls to set up Eups and ReposYaml need protecting; the calls to Jira should be safe.