ZNC start script fix

Hi,

I had to change the start script in the following way:

`/var/packages/znc/scripts/start-stop-status`:

```sh
# Originally:
#su ${USER} -c "${ZNC} -d ${INSTALL_DIR}/var"

# Now:
sudo -u ${USER} -EH -i -- sh -c "${ZNC} -d ${INSTALL_DIR}/var"
```

Su didn't work for me as znc user was not in /etc/shadow, I've always got permission denied. Maybe this could be stated in the README.

This actually fixes a problem with starting ZNC from Synology.

Thanks!