Apparmor disabling NTP because of missing line in ntp apparmor config file for leapseconds

This fix was added to deal with the issue where apparmor disables ntp:

[9789856.669346] type=1400 audit(1373675824.822:19): apparmor="DENIED" operation="open" parent=1 profile="/usr/sbin/ntpd" name="/etc/ntp.leapseconds" pid=1884 comm="ntpd" requested_mask="r" denied_mask="r" fsuid=0 ouid=0