Otherwise it may start too early and end up taking 10.0.3.1 even
though eth0 was eventually going to end up on 10.0.3.x.

https://bugs.launchpad.net/juju-core/+bug/1510619Reported-by: Ryan Harper <ryan.harper@ubuntu.com>
Cc: Martin Pitt <martin.pitt@ubuntu.com>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>