Docker create network should ignore existing network

You can first test for the existence of the network, and create it if it doesn't exist. For example:

docker network ls|grep my_local_network > /dev/null || echo "network does not exist"

Replace the echo with your network create command:

docker network ls|grep my_local_network > /dev/null || docker network create --driver bridge my_local_network

Building on @AndyTriggs' answer, a neat (and correct) solution would be:

docker network inspect my_local_network >/dev/null 2>&1 || \
    docker network create --driver bridge my_local_network

Currently there is no way to force it OR ignore it but you can get rid of this problem using shell -

docker network create --driver bridge my_local_network || true

This way whenever your build script executes, if there is no network it will create one else it will return true without any command failure so that rest of the build script can execute.