Missing make rule for test/fixtures/keys/0-dns-*

[kapouer]

Part of ssl 1.1.0 transition will require to rebuild old certificates fixtures
to use stronger encryption, and i don't find how to rebuild those files.

[addaleax]

@indutny

[sam-github]

I skimmed #8491, and don't understand why a new ossl should require cert rebuild. Please explain.

However, it would be good if the Makefile built all the certs, and it doesn't. It would be even nicer if it only build the ones that were missing... so that it was easy to add new cert variants without regenerating the root keys and rebuilding their certs.

Unfortunately, ossl doesn't seem capable of building certs completely from CLI args, it needs custom config files. I've been poking at this a bit, but haven't had the time to get anywhere (I want more certs issued by sub-CAs, among other things).

[kapouer]

The reason is simple, openssl throw errors about using too short keys, so new, longer keys, must be regenerated.