Previously, the snap set up a bridge using the default 10.20.20.0/24
network upon install. If there was a good reason not to use this
network (e.g., it already exists and is being used for another
purpose), MicroStack, and the host machine, could wind up in a broken
state.
This PR delays setting up the bridge until after we have given an
operator a chance to override the default settings.
This has been manually tested. To test, do the following:
1) Checkout the code, and run tox -e build
2) Run tools/make-a-microstack.sh
3) snapctl set config.network.ext-cidr and config.network.ext-gateway
4) Run microstack_init
5) Exit the snap shell and run microstack.launch
Change-Id: I9e268495f313b29d9781d80a2468fc0a1a450aa0
Closes-Bug: https://bugs.launchpad.net/microstack/+bug/1851521