Description of problem:
In the containerized undercloud re-run removes the undercloud_admin_host and undercloud_public_host ip addresses if config for os-net-config is changed.

The br-ctlplane interface is restarted by os-net-config and this removes the undercloud_admin_host and undercloud_public_host ip addresses set up by keepalived. The install/update operation fails later on because services fail to connect to the ip that is no longer there.

Version-Release number of selected component (if applicable):
Upstream current-dev used when I found the bug.

How reproducible:
100%

Steps to Reproduce:
1. Deploy undercloud
2. Change the undercloud_nameservers address in undercloud.conf

sed -i s/undercloud_nameservers = <old-address>/undercloud_nameservers = <new-address>/g /home/stack/undercloud.conf

3. Re-run undercloud install

openstack undercloud install

Additional reproducer:
----------------------

1. Deploy undercloud with routed networks enabled
2. Add more subnets to prepare the undercloud for scale out to additional routed networks leafs
3. Re-run the undercloud installer

  Because additional routes for the ctlplane network traffic is added, this causes os-net-config to re-run as well. And the restart of br-ctlplane kill's the VIP's.


Actual results:
Undercloud update fails.

Expected results:
Undercloud update should succeed.

Additional info:


1. The os-net-config is config.json is updated with the new dnsserver.

Every 5.0s: diff -aur /etc/os-net-config/config.json /tmp/os-net-config.json.orig                                                                                                          Fri Sep  7 08:51:26 2018

--- /etc/os-net-config/config.json      2018-09-07 08:45:39.054174371 +0200
+++ /tmp/os-net-config.json.orig        2018-09-07 08:17:38.597808977 +0200
@@ -1 +1 @@
-{"network_config": [{"addresses": [{"ip_netmask": "172.20.0.200/26"}], "dns_servers": ["192.168.122.1"], "members": [{"mtu": 1500, "name": "eth1", "primary": true, "type": "interface"}], "name": "br-ctlplane",
"ovs_extra": ["br-set-external-id br-ctlplane bridge-id br-ctlplane"], "routes": [], "type": "ovs_bridge", "use_dhcp": false}]}
+{"network_config": [{"addresses": [{"ip_netmask": "172.20.0.200/26"}], "dns_servers": ["172.20.0.254"], "members": [{"mtu": 1500, "name": "eth1", "primary": true, "type": "interface"}], "name": "br-ctlplane", "
ovs_extra": ["br-set-external-id br-ctlplane bridge-id br-ctlplane"], "routes": [], "type": "ovs_bridge", "use_dhcp": false}]}

2. After os-net-config applied config the keepalived VIPs are gone:

Every 2.0s: ip addr show br-ctlplane                                                                                                                                                       Fri Sep  7 08:51:08 2018

47: br-ctlplane: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default qlen 1000
    link/ether 52:54:00:7a:f6:c5 brd ff:ff:ff:ff:ff:ff
    inet 172.20.0.200/26 brd 172.20.0.255 scope global br-ctlplane
       valid_lft forever preferred_lft forever
    inet6 fe80::5054:ff:fe7a:f6c5/64 scope link
       valid_lft forever preferred_lft forever

3. The upgrade is stuck on starting the containers:

TASK [Start containers for step 3] **********************************************

4. Log's show that services are failing to connect to the database via the keepalived VIPs:

/var/log/containers/nova/nova-compute.log:2018-09-07 08:52:47.462 6 ERROR oslo_service.periodic_task RemoteError: Remote error: DBConnectionError (pymysql.err.OperationalError) (2003, "Can't connect to MySQL server on '172.20.0.201' ([Errno 113] EHOSTUNREACH)") (Background on this error at: http://sqlalche.me/e/e3q8)