Ticket/master/pdb 954 fallback acceptance

Here's one we don't catch:

```
Error: Failed to submit 'replace facts' command for kb.local to PuppetDB at puppetdb1.vm:8081: [404 Not Found] Not Found
```

Think about the slow startup case we have with PuppetDB, where jetty is around but not yet started. I faked this by adding /foo at the end of a server_url entry ... probably worth adding the to acceptance also /cc @wkalt