Wrong information about DNS resolution in admin guide

[Dr. Jens Harbott]

In the section "Name resolution for instances" (doc/source/admin/config-dns-res.rst) the functional description for case 2 and 3 is wrong.

In both cases, the DHCP agents do not offer the mentioned IP addresses to the instances. Instead, the DHCP agents offer the list of IP addresses of DHCP agents in the respective subnet to the instances in that subnet. The DHCP agents then run dnsmasq as a forwarding and masquerading resolver, forwarding DNS requests from the instances to the configured IP addresses, i.e. to the ones configured in ``dnsmasq_dns_servers`` in case 2 and to the ones configured in ``/etc/resolv.conf`` on the host in case 3.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/504349

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/504349
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=59f5e37ff419af33bc7dbffd35ef98e6990dec24
Submitter: Zuul
Branch: master

commit 59f5e37ff419af33bc7dbffd35ef98e6990dec24
Author: Jens Harbott <email address hidden>
Date: Tue Sep 12 11:23:06 2017 +0000

    Fix documentation for DNS resolver config

    We need to correctly describe what is really happening: The dnsmasq
    processes in the DHCP agent act as forwarding masquerading resolvers for
    the instances in their particular subnets.

    Change-Id: I50ef9f488eb1efb8f709b75537ca4a4e9efce75a
    Closes-Bug: 1715842

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/neutron 12.0.0.0b1 development milestone.