Sometimes we would like to create a base image without any DB access, this
assists in creating custom base images with custom plugins that already
includes `public/assets`
Following this change set you can run:
```
SPROCKETS_CONCURRENT=1 DONT_PRECOMPILE_CSS=1 SKIP_DB_AND_REDIS=1 RAILS_ENV=production bin/rake assets:precompile
```
Then it is straight forward to create a base image without needing a DB or
Redis.