designate-bind needs extra binding support

[Nobuto Murata]

designate-bind currently has dns-backend:bind-rndc relation so we can specify which network to accept rndc command from designate control plane. designate-bind is to be exposed for clients outside of a Juju model for actual name resolution, but we don't have a way to add an extra network to accept dns queries.

Would be nice to have an extra binding support in the charm.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/585944

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/585944
Committed: https://git.openstack.org/cgit/openstack/charm-designate-bind/commit/?id=af9f3e79b560776ba3640d987dffb173c9504b5c
Submitter: Zuul
Branch: master

commit af9f3e79b560776ba3640d987dffb173c9504b5c
Author: Nobuto Murata <email address hidden>
Date: Thu Jul 26 13:23:55 2018 +0900

    Add dns-frontend extra binding

    Another network space can be added to offer DNS service to clients
    outside of the Juju model.

    Change-Id: Ida1dd81bc4e2a2f1778ffa5d747a88c860164def
    Closes-Bug: #1783678