I recently had to make running snaps inside docker containers work and blogged about it here
You can grab the setup script (Dockerfile inside) at https://github.com/ogra1/snapd-docker
Please note that this should not be used in sensible production environments.
The setup of the container disables apparmor and seccomp inside the container and snaps might be able to break out of their confinement into the container.
That said, I think it will still be helpful for development or functional tests in a self maintained CI setup at home. Which is why i left this post here.