When a dynamic_address_gather_filter is set and the inventory
data does not generate the dynamic inventory variable
container_networks[network_address]['bridge'], the task will
fail, as even though dynamic_address_gather_filter is defined
the jinja template will still try to evaluate
container_networks[network_address]['bridge'].
This patch fixes this by setting a default value if
container_networks[network_address]['bridge'] is not defined
Change-Id: I39082bee2435781d87f653e66fd55a92397c5572
3504694b4a