postgres recipe: on update or re-install generate configuration and wrapper file

If pgdata already exists, then postgres recipe will not update or install anything when buildout will run. This result to no configuration or wrapper updated if configuration changes.

For example this change:  29d1ed68  the path of `posgtres bin` is now in shared folder, then impossible to run postgres service anymore because path was not updated by buildout in wrapper.

/reviewed-on !703