Added possibility to use an existing config file for recursor or auth…

[murphy83]

Idea to have the option to use an already existing (eg. externally generated) config file for recursor or authorative power-dns-mysql).
The behavior is controlled by setting the environment variable USE_EXISTING_CONFIG_FILE to "true". Disabled by default.

[pschiffe]

Hello @murphy83 , thank you for your contribution. I'm OK with this change, however, could you update also the pdns-pgsql image, so both images (pdns-pgsql and pdns-mysql) are equal feature-wise? Thank you.

[murphy83]

I was thinking about this idea already, however I am still not 100% sure about the path to follow, as usually refrain from "just duplicating code". So I am a bit tempted to use something like a functions-file to include for the parts that are valid for both Postgres and MySQL/MariaDB.
Let me know what you think fits better in your opinion.

[pschiffe]

Feel free to do what you prefer. I've kept it separate as it's really not that much code, it's fairly simple and not updated that often.

[murphy83]

OK I think I will set to work on this in the evening.

[murphy83]

Indeed ... this function was defined but never called ...