Code review comment for lp:~vishvananda/nova/lp710959

> * I couldn't verify whether the changes impacted IPv6. Specifically the following line:
> 206 if(FLAGS.use_ipv6):
> 207 _execute("sudo ip -f inet6 addr change %s dev %s" %
> 208 (net_attrs['cidr_v6'], bridge))
> I'm not sure if this can be run more than once without throwing an error.

I wrote above codes to fix bug #707908.
As you know, each network interfaces can have more than one ipv6 addresses.
When some interface A already has ipv6 address B
 "sudo ifconfig A add B"　throws the "SIOCSIFADDR: File exists" error.
 "sudo ip -f inet6 addr change B dev A"　does nothing without throwing the error.
And when interface A does not have address B
 "sudo ip -f inet6 addr change B dev A" adds address B to A.