Generate the DH parameters, remove burp.ssl.DH, improve Buster support
- remove the mandatory parameter
burp.ssl.DH
- generate the DH parameters when needed
- add a role default parameter
burp_dh_size
- Debian Buster: don't use the workarounds no longer required
- CI: fix Stretch tests (Buster was used instead of Stretch)
Resolves: #2 (closed)