scripts/linuxcnc.in: set default for MACHINEKIT_INI

user may override this by 'export MACHINEKIT_INI=<path>'
scripts/realtime.in: point MACHINEKIT_INI to installed default unless overridden

normally realtime would inherit MACHINEKIT_INI from scripts/linuxcnc but it
might be called standalone as well so assure a sensible setting is in place
tests/halui-jogging: disable