Comment 4 for bug 1915278

Seeing this in CI:
2021-05-19 10:09:15 | 2021-05-19 10:09:15.645868 | fa163e71-6144-8ff9-b04c-0000000011f4 | FATAL | Check Default IPv4 Gateway availability | overcloud-controller-2 | error={"changed": false, "cmd": ["ping", "-w", "10", "-c", "1", "10.0.0.1"], "delta": "0:00:03.095271", "end": "2021-05-19 10:09:15.616717", "msg": "non-zero return code", "rc": 1, "start": "2021-05-19 10:09:12.521446", "stderr": "", "stderr_lines": [], "stdout": "PING 10.0.0.1 (10.0.0.1) 56(84) bytes of data.\nFrom 10.0.0.10 icmp_seq=1 Destination Host Unreachable\nFrom 10.0.0.10 icmp_seq=2 Destination Host Unreachable\nFrom 10.0.0.10 icmp_seq=3 Destination Host Unreachable\n\n--- 10.0.0.1 ping statistics ---\n3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2061ms\npipe 3", "stdout_lines": ["PING 10.0.0.1 (10.0.0.1) 56(84) bytes of data.", "From 10.0.0.10 icmp_seq=1 Destination Host Unreachable", "From 10.0.0.10 icmp_seq=2 Destination Host Unreachable", "From 10.0.0.10 icmp_seq=3 Destination Host Unreachable", "", "--- 10.0.0.1 ping statistics ---", "3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2061ms", "pipe 3"]}

https://logserver.rdoproject.org/31/792031/3/openstack-check/tripleo-ci-centos-8-ovb-3ctlr_1comp-featureset001/861d6e7/logs/undercloud/home/zuul/overcloud_deploy.log.txt.gz

Undercloud interface looks ok:
https://logserver.rdoproject.org/31/792031/3/openstack-check/tripleo-ci-centos-8-ovb-3ctlr_1comp-featureset001/861d6e7/logs/undercloud/var/log/extra/network.txt.gz

4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc fq_codel state UP group default qlen 1000
    inet 10.0.0.1/24 brd 10.0.0.255 scope global eth2
       valid_lft forever preferred_lft forever

overcloud-controller-2 networks looks ok:
https://logserver.rdoproject.org/31/792031/3/openstack-check/tripleo-ci-centos-8-ovb-3ctlr_1comp-featureset001/861d6e7/logs/overcloud-controller-2/var/log/extra/network.txt.gz

9: br-ex: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1350 qdisc noqueue state UNKNOWN group default qlen 1000
    inet 10.0.0.10/24 brd 10.0.0.255 scope global br-ex
       valid_lft forever preferred_lft forever

### IPv4 routing
default via 10.0.0.1 dev br-ex