dnsmasq should run in "authoritative mode"

[Alexey I. Froloff]

When dnsmasq is restarted, it forgets about all leases (since it runs with leasefile-ro option). When client tries to renew its lease, dnsmasq sends DHCPNAK reply with message "lease not found". Then client shuts down the network and re-request lease from DHCP server (and gets exactly same IP address). There's a small network downtime which affects services, like zookeeper, running in VMs.

dnsmasq have special option, --dhcp-authoritative, which makes it think it's the only DHCP server on network. In this particular case, when lease not found and client renews address, operation is completed successfully. Although, several DHCP agents may exist for a single network, they all share same configuration and can be considered as "the only DHCP server".

TL;DR - option "--dhcp-authoritative" should be added to dnsmasq's command line.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/152080