switch to using dns_domain_ports extension driver for >= queens

[Edward Hope-Morley]

Openstack Queens and above support the new dns_domain_ports extension driver [1] which extends the current dns driver to allow setting a dns_domain on ports that can override that set on their network. This is useful when implementing external dns integration [2].

[1] https://docs.openstack.org/neutron/queens/admin/config-dns-int.html
[2] https://docs.openstack.org/neutron/queens/admin/config-dns-int-ext-serv.html

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/635667

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/635667
Committed: https://git.openstack.org/cgit/openstack/charm-neutron-api/commit/?id=4c842b134601a7ba077e9b8445ca297ab946f5d6
Submitter: Zuul
Branch: master

commit 4c842b134601a7ba077e9b8445ca297ab946f5d6
Author: Edward Hope-Morley <email address hidden>
Date: Thu Feb 7 22:01:27 2019 +0000

    Use dns_domain_ports extension driver for >= queens

    The dns_domain_ports extension driver was introduced in Queens
    to allow setting a dns_domain on ports and having that
    override the network dns_domain value. The new extension driver
    inherits from the old dns extension driver so it is safe to
    simply replace it.

    Change-Id: I26db4433359cf8c9d23158d553c4805fd0526a1a
    Closes-Bug: #1815138