Removed trailing whitespaces with

```sh
for file in `grep -r " $" * | cut -d : -f 1 | sort | uniq | grep -v " "`; do sed -i 's/[ \t]*$//' $file; done
```

and some handwork.

Replace the host with $DB_PORT, which is dependent to the database imagae's exposed port.

Replace the 'mysql' options with 'db' options, makeing the config according to the database type.