apparmor blocks bind9 from reading rndc.key

[Yaro Kifor]

- [X] This doc is inaccurate in this way: Doc neglects apparmor existences which can lead to a broken configuration.
- [ ] This is a doc addition request.
- [X] I have a fix to the document that I can paste below including example: Operators need to make sure that apparmor is disabled or configured correctly to allow for bind9 to access /etc/designate/rndc.key. This line needs to be add to /etc/apparmor.d/usr.sbin.named: "/usr/bin/named { ... /etc/designate/rndc.key r, }" for bind9 to start correctly.

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-----------------------------------
Release: 5.0.0.0rc2.dev7 on 2017-08-22 12:57
SHA: e85f89a3a72b3efde921bff71af36400e5855704
Source: https://git.openstack.org/cgit/openstack/designate/tree/doc/source/install/install-ubuntu.rst
URL: https://docs.openstack.org/designate/latest/install/install-ubuntu.html