sanitize_hostname is not alligned with idna2 specification

[Vasyl Saienko]

DNSmask was switched to IDN2 specification more than 4 year ago Debian package [0]
According to specification name with -- in 3rd and 4th characters is not allowed. See RFC 5891 [1]
As result hostnames for example (rf--xx), generates error on DNSmasq side, and no longer works

Aug 29 10:55:32 dnsmasq[243]: bad DHCP host name at line 2 of /var/lib/neutron/dhcp/6531ba54-0aa1-4b3b-b098-49bb0cfd586b/host

cat /var/lib/neutron/dhcp/6531ba54-0aa1-4b3b-b098-49bb0cfd586b/host
fa:16:3e:d9:ba:17,amphora-ccee6c76-e565-496d-b841-f485a99dc865.openstack.internal.,10.10.10.142
fa:16:3e:c8:93:56,re--test-database-7ezitojxojun-server-01-lrdygbkrxkho.openstack.internal.,10.10.10.209
fa:16:3e:29:dc:fc,host-10-10-10-45.openstack.internal.,10.10.10.45
fa:16:3e:1a:be:3f,host-10-10-10-103.openstack.internal.,10.10.10.103
fa:16:3e:bd:ab:2a,host-10-10-10-1.openstack.internal.,10.10.10.1
fa:16:3e:df:b7:c1,host-10-10-10-118.openstack.internal.,10.10.10.118

[0] https://github.com/imp/dnsmasq/commit/5a9133498562a0b69b287ad675ed3946803ea90c
[1] https://www.rfc-editor.org/rfc/rfc5891#section-4.2.3.1

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/nova/+/893072