Fix patch "Wait for external bridge"
Fix patch "Wait for external bridge"

An inactive version of the patch "Wait for external bridge" got somehow
submitted for review and merged. This patch enables the code.

Change-Id: I1212d2a4c9bc899c258941acc0022207c4370db3

openstack/training-labs,dguitarbite/OpenStack-Labs,openstack/training-labs,dguitarbite/OpenStack-Labs,openstack/training-labs,dguitarbite/OpenStack-Labs