dnsmasq fails to respond if hostname length is > 63

[Simon Pasquier]

nova-network generates invalid entries in the dnsmasq hosts file when the hostname of the instance is longer than 63 characters.

$ cat /opt/stack/data/nova/networks/nova-br100.conf
fa:16:3e:6c:93:03,testvm1.novalocal,10.0.0.2
fa:16:3e:50:95:a8,testvm1hejazkhejkazehjzakhejazklehazjklehazjklehazjklehazjkelhazjelhazjelhazjeklazhejklazhejkazlehjazklehazjklehazjkelhazjeklazhej.novalocal,10.0.0.3

$ grep dnsmasq /var/log/syslog
Oct 16 12:12:22 r421-e3-4 dnsmasq-dhcp[15975]: DHCPDISCOVER(br100) fa:16:3e:6c:93:03
Oct 16 12:12:22 r421-e3-4 dnsmasq-dhcp[15975]: DHCPOFFER(br100) 10.0.0.2 fa:16:3e:6c:93:03
Oct 16 12:12:24 r421-e3-4 dnsmasq-dhcp[15975]: DHCPDISCOVER(br100) fa:16:3e:50:95:a8 no address available

As per RFC 1035:
The labels must follow the rules for ARPANET host names. They must
start with a letter, end with a letter or digit, and have as interior
characters only letters, digits, and hyphen. There are also some
restrictions on the length. Labels must be 63 characters or less.

The problem was found while investigating bug #1238272.