Fix live migration to use migration int. address

In kolla ansible we typically configure services to communicate via IP
addresses rather than hostnames. One accidental exception to this was
live migration, which used the hostname of the destination even when
not required (i.e. TLS not being used for libvirt).

To make such hostnames work, k-a adds entries to /etc/hosts in the
bootstrap-servers command. Alternatively users may provide DNS.

One problem with using /etc/hosts is that, if a new compute host is
added to the cloud, or an IP address is changed, that will not be
reflected in the /etc/hosts file of other hosts. This would cause live
migration to the new host from an old host to fail, as the name cannot
be resolved.

The workaround for this was to update the /etc/hosts file (perhaps via
bootstrap-servers) on all hosts after adding new compute hosts. Then the
nova_libvirt container had to be restarted to pick up the change.

Similarly, if user has overridden the migration_interface, the used
hostname could point to a wrong address on which libvirt would not
listen.

This change adds the live_migration_inbound_addr option to nova.conf. If
TLS is not in use for libvirt, this will be set to the IP address of the
host on the migration network. If TLS is enabled for libvirt,
live_migration_inbound_addr will be set to migration_hostname, since
certificates will typically reference the hostname rather than the
host's IP. With libvirt TLS enabled, DNS is recommended to avoid the
/etc/hosts issue which is likely the case in production deployments.

Change-Id: I0201b46a9fbab21433a9f53685131aeb461543a8
Closes-Bug: #1729566
(cherry picked from commit 628c27ce9e)

ansible/roles/nova/templates/nova.conf.d/libvirt.conf.j2

@@ -1,5 +1,6 @@
 [libvirt]
 connection_uri = "qemu+tcp://{{ migration_interface_address }}/system"
+live_migration_inbound_addr = "{{ migration_interface_address }}"
 {% if enable_ceph | bool and nova_backend == "rbd" %}
 images_type = rbd
 images_rbd_pool = {{ ceph_nova_pool_name }}

releasenotes/notes/bug-1729566-8b77402fd8236962.yaml

@@ -0,0 +1,13 @@
+---
+fixes:
+  - |
+    Fixes an issue with Nova live migration not using
+    ``migration_interface_address`` even when TLS was not used.
+    When migrating an instance to a newly added compute host, if addressing
+    depended on ``/etc/hosts`` and it had not been updated on the
+    source compute host to include the new compute host, live migration would
+    fail. This did not affect DNS-based name resolution.
+    Analogically, Nova live migration would fail if the address in
+    DNS/``/etc/hosts`` was not the same as ``migration_interface_address``
+    due to user customization.
+    `LP#1729566 <https://bugs.launchpad.net/kolla-ansible/+bug/1729566>`__