Using .local as TLD in dns testing is breaking some scenarios

[Dr. Jens Harbott]

Neutron tempest and devstack OVN setup use "openstackgate.local" as dns_domain, which is leading to failures in some scenarios, since .local is reserved to be used as mdns domain, and thus some resolvers like the one in systemd do not query global DNS for records in this zone.

How to reproduce:

Deploy devstack with the q-dns service enabled (or set dns_domain = openstackgate.local in neutron.conf manually).

Create servers named s1 and s2 in the same network.

Log into s1 and run some testing:

```
debian@s1:~$ host s2
s2 has address 10.0.0.74
s2 has IPv6 address fd6d:c2ac:91ec:1:f816:3eff:fe76:ae24
Host s2 not found: 3(NXDOMAIN)
debian@s1:~$ host 10.0.0.74
74.0.0.10.in-addr.arpa domain name pointer s2.openstackgate.local.
debian@s1:~$ ping 10.0.0.74 -c2
PING 10.0.0.74 (10.0.0.74) 56(84) bytes of data.
64 bytes from 10.0.0.74: icmp_seq=1 ttl=64 time=1.12 ms
64 bytes from 10.0.0.74: icmp_seq=2 ttl=64 time=0.980 ms

--- 10.0.0.74 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1002ms
rtt min/avg/max/mdev = 0.980/1.048/1.116/0.068 ms
debian@s1:~$ ping -c3 s2
ping: s2: Name or service not known
debian@s1:~$ ping s2.openstackgate.local
ping: s2.openstackgate.local: Temporary failure in name resolution
debian@s1:~$

```

Using a different dns_domain like example.org makes the last ping example work.

[Dr. Jens Harbott (j-harbott)]

References in neutron/devstack code:

https://opendev.org/openstack/neutron/src/branch/master/devstack/lib/dns#L17
https://opendev.org/openstack/neutron-tempest-plugin/src/branch/master/neutron_tempest_plugin/config.py#L77
https://opendev.org/openstack/devstack/src/branch/master/lib/neutron_plugins/ovn_agent#L495