by default we don't set nameserver when setting up neutron subnet used
by overcloud nodes, then nameserver points to the machine where
undercloud's dnsmasq is running.
I wonder if we should not change *default* devtest setup to allow dns
resolving not only for local network but for internet? Proper DNS
resolving is handy e.g. for package update scenario.
This would mean:
a) set explicitly nameserver when configuring neutron subnet (as it's
done for network in overcloud )
b) set forwarding dns server for dnsmasq 
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