fix missing MACHINEKIT_INI default + export, /var/log/linuxcnc.log permissions + logging

I hope this covers most of the open issues

however, I do not understand why /etc/linuxcnc/machinekit.ini is not carried over into the package; rtapi.ini - which is in the same directory - shouldnt this be covered by: https://github.com/machinekit/machinekit/blob/master/debian/machinekit.install#L1 ?