run dh_installinit

In order to make naemon reboot safe. Shipping a rc file named naemon-core.naemon.init
seems to copy the file in the right place, but dh_installinit does not look in that
place. So explictily run dh_installinit by rules file.

Signed-off-by: Sven Nierlein <Sven.Nierlein@consol.de>