fix multiple domains

[MichaelSp]

Things like *.example.org is a valid entry for dokku vhost but is not supported by letsencrypt.

[sseemayer]

Thank you very much for your pull request! Before I merge this, would you mind fixing two small things?

• If only a wildcard domain is configured as an app's URL, it will be filtered out and the letsencrypt client will be started without specifying a domain argument. Instead, we should fail with an error message.
• Filtering out a wildcard domain should be shown to the user in a log message so they can tell what's going on. It might be possible to use the loop for constructing the domain arguments to give such a warning message.

[MichaelSp]

I think there is a misconception about what this line does.
Here is an examples to understand this:

Suppose we have the following vhosts:
http://www.example.com *.other-example.org other-example.org
will be modified to
www.example.com other-example.org.

The provided regex just removes duplicates.
I don't think it is valid or possible to define * as vhost.

[sseemayer]

Then I indeed had misconceptions about the patch - I thought the intent was to completely remove the URLs containing wildcards but reading the regular expression again plus your comment helped. Thanks!

As far as I read the dokku nginx-vhosts, domains and certs plugins, any string is a valid domain for the purposes of the plugins and will be passed into a server_name entry in the generated nginx configs. Since the wildcard domain doesn't match any of the names in the installed certificate and will thus not be returned by the get_ssl_hostnames function, the nginx-vhosts plugin will generate a non-https server entry. I guess that's the best we can do for the case of wildcard domains.

[sseemayer]

Also, many thanks for the PR!