Update neutron_dnsmasq_dns_servers parameter name

Refs: https://github.com/enovance/puppet-openstack-cloud/pull/735
and https://github.com/openstack/neutron/commit/a269541c603f8923b35b7e722f1b8c0ebd42c95a
Merge pull request #21 from enovance/neutron-dns

Update neutron_dnsmasq_dns_servers parameter name