Re: pg_hosts: Add pg_hosts_file_rules()

> I think it's a good idea to add this. One thing I have been puzzling over is
> what to do with LibreSSL builds which don't support ssl_sni. One could argue
> that parsing the file doesn't require ssl_sni actually function, so the view
> could still work, but on the other hand it might be confusing to users to learn
> that their file doesn't generate any errors yet ssl_sni doesn't work. I think
> I prefer if the view is blank and the file isn't parsed in clusters which
> doesn't support ssl_sni. What are your thoughts on that?

I agree, I was already thinking about this in more general ways as
part of the config rework (what else could be in pg_hosts), but for
the context of this patch it's better to limit it similarly to the
main feature.

Should I also try to add a liressl specific test to it?

I also addressed the other comments, except:

> This test doesn't need the ->reload command here does it, since the view parses
> whats on the filesystem and not what's running. Also, since we know the view
> shall have a single row with an error we should test for == 1 instead of >= 1.
> Similarily, the previous test doesn't need to restart the cluster?

The first is needed, or we need at least start, as postgres is stopped
before it (previous test fails the restart).

Attached v2.