grizzly: new options for managing multi-host network

[Tom Fifield]

If https://review.openstack.org/#/c/16153 is merged, there are some new features in grizzly for DNS and DHCP networking, especially with multi host.

Currently this includes at least one new option: update_dns_entries

    Configure all dnsmasq instances to use the hosts file instead of the
    default local file '/etc/host' when the network is configured in
    'multi_host' mode.

    This hosts file contains all DNS entries of the network and it is
    replicated on all host where a 'nova-network' daemon is instantiated.
    There is a hosts file for each networks.

    It needs to add a new network API to update the host file on all
    network hosts.

    When a network host is called to (de)allocate a VM, it (de)allocate the
    instance fixed IP adress(es) on the concerned network host and when it's
    done, it calls all networks to update their DNS db entries if it's
    needed through a fanout cast.

    DocImpact: new config options
    Fixes LP bug #1078808

[Tom Fifield (fifieldt)]

patch was merged

[Tom Fifield (fifieldt)]

now in config reference