Fix appamor configuration for Ubuntu

Since at least Ubuntu 14.04, I saw lot of errors in syslog :
```
[4542988.686845] type=1400 audit(1416405833.983:2260): apparmor="DENIED" operation="open" profile="/usr/sbin/ntpd" name="/usr/local/sbin/" pid=11667 comm="ntpd" requested_mask="r" denied_mask="r" fsuid=0 ouid=0
[4542988.686856] type=1400 audit(1416405833.983:2261): apparmor="DENIED" operation="open" profile="/usr/sbin/ntpd" name="/usr/local/bin/" pid=11667 comm="ntpd" requested_mask="r" denied_mask="r" fsuid=0 ouid=0
[4542988.686863] type=1400 audit(1416405833.983:2262): apparmor="DENIED" operation="open" profile="/usr/sbin/ntpd" name="/usr/sbin/" pid=11667 comm="ntpd" requested_mask="r" denied_mask="r" fsuid=0 ouid=0
[4542988.686869] type=1400 audit(1416405833.983:2263): apparmor="DENIED" operation="open" profile="/usr/sbin/ntpd" name="/usr/bin/" pid=11667 comm="ntpd" requested_mask="r" denied_mask="r" fsuid=0 ouid=0
[4542988.686875] type=1400 audit(1416405833.983:2264): apparmor="DENIED" operation="open" profile="/usr/sbin/ntpd" name="/sbin/" pid=11667 comm="ntpd" requested_mask="r" denied_mask="r" fsuid=0 ouid=0
[4542988.686882] type=1400 audit(1416405833.983:2265): apparmor="DENIED" operation="open" profile="/usr/sbin/ntpd" name="/bin/" pid=11667 comm="ntpd" requested_mask="r" denied_mask="r" fsuid=0 ouid=0
```
After comparing the apparmor configuration from Ubuntu and the one in the ntp cookbook, I saw that two rules are missing.