Support newer database plugin list formats

[palfrey]

• https://github.com/dokku/dokku-postgres/commit/4dc758d7e6fdafd2b0aff030b0e6492022b9c4a5 in Postgres >=1.10.0 broke Wharf because we want the data from "postgres:list"
• https://github.com/dokku/dokku-redis/commit/bc9874bc49bc1933ef590cb2a94b10e32cf49852 in Redis >= 1.11.0 similarly broke "redis:list"

[KTachibanaM]

Hello. I would like to work on this. I do wonder if we want to worry about keeping backwards compatibility with older versions of plugins?

[palfrey]

Hello. I would like to work on this. I do wonder if we want to worry about keeping backwards compatibility with older versions of plugins?

I'd ideally like to support both forms. If it it turns out they've changed it again or something I'd probably revise that, but I'd like to avoid breaking all existing users (e.g. my own site!). I'm hoping that shouldn't be too hard, but feel free to flag if I\m wrong there.