https://github.com/docker-library/postgres/issues/1024 converted all
`echo` calls to `printf`, but this change causes the password file
used by `initdb` to be blank rather than contain a single newline.
As a result, `initdb` will fail to start with an empty value with
the error:
```
initdb: error: password file "/dev/fd/63" is empty
```
`POSTGRES_PASSWORD` can be blank if `POSTGRES_HOST_AUTH_METHOD=trust`
is used. This change adds a newline to restore the original behavior.
Closes#1025
The use of the `echo` shell built-in has been actively discouraged for a long time, but it's really convenient so we keep doing it. This converts them all to use `printf` appropriately such that we avoid issues like `echo "$someVar"` from doing the wrong thing if `$someVar` is `-n` or similar.
We were already checking for whether `POSTGRES_DB` was set to `postgres`, but this was the underlying motivation for that check (and it turns out that this applies for values of at least `template0` and `template1` as well).
Add POSTGRES_HOST_AUTH_METHOD to bring back old behavior and be similar to MYSQL_ALLOW_EMPTY_PASSWORD, but add warning when "trust" is used since it disables all passwords
Stan Hu