cloud-init-test is here:

https://code.launchpad.net/~raharper/+git/cloud-init-test

After checking out, you need to populate the main dir with a copy of cloud-init deb you want to inject

cp /path/to/cloud-init_all.deb cloud-init-py3.deb

You need to have your new cloud-utils network branch built and install the cloud-image-utils update
so we can call cloud-localds with --network-config= 

Then you can

nosetests3 -vv --nologcapture tests/vmtests/test_network.py:XenialTestNetworkStatic

This will do streams mirror to pull it down,
It will sudo prompt you when it runs mount-image-callback to inject updated cloud-init deb into an image.

Currently it doesn't parse/see the seed.img; that needs to be debugged; why new cloud-init doesn't read/parse the seed.img injected as a /dev/vdc.

In tests/vmtests/__init__.py  there is a new class CloudInitVMBaseClass that contains the changes to the init process, mostly new variables to pass to the tools/inject-cloud-init  which tars up payload dir in cloud-init-test dir.