Fix sed in run-os-net-config to only replace values, not keys
Fix sed in run-os-net-config to only replace values, not keys

The sed in run-os-net-config.sh replaces all instances of bridge_name
but it should only replace values, not keys.

Change-Id: Iaf19e1550bd7a5286b8512596efd84cf14c78f32
Closes-bug: #1854780

openstack/tripleo-heat-templates,openstack/tripleo-heat-templates