[admin-guide] Adding distinction between instance and interface
[admin-guide] Adding distinction between instance and interface

Change-Id: I477455c3dfda95b084e723c14438e1e83a6ac6f4
Closes-bug: 1464423

openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals