Improve ip address detection for multinode test on OS X
Improve ip address detection for multinode test on OS X

The original way could pick up a bridge interface, this way we filter
out only actual interfaces.

h2oai/h2o-3,h2oai/h2o-3,h2oai/h2o-3,h2oai/h2o-3,h2oai/h2o-3,h2oai/h2o-3,h2oai/h2o-3,h2oai/h2o-3