Can't install vsftpd because of pkg_postinstall

When trying to add vsftpd to an image I get this error: 

```
Postinstall scriptlets of ['vsftpd'] have failed. If the intention is to defer them to first boot,
then please place them into pkg_postinst_ontarget_${PN} ().
Deferring to first boot via 'exit 1' is no longer supported.
```

I tried to split the code as the error says but still not working.
