feat: implement the driver's package, doctor, and status hooks

[tas50]

Kitchen::Driver::Base defines three hooks for a driver to answer questions the CLI asks. This driver inherited all three unimplemented, so all three answered with a shrug:

$ kitchen package default-ubuntu-2404
-----> Packaging remote instance          # and nothing was produced

$ kitchen doctor default-ubuntu-2404
-----> The doctor is in                   # and nothing was checked

$ kitchen list --live
Instance             Driver  ... Last Action  Last Error  Live Status
default-ubuntu-2404  Docker  ... Created      <None>      unknown

Docker can answer all three.

package

Commits the container to an image — the artifact every other docker tool already takes. docker save gets a tarball from it.

-----> Packaging remote instance
       [Docker] Packaged default-ubuntu-2404 as default-ubuntu-2404:latest (sha256:1f51c590...)

Named after the instance by default (already lowercase and dash-separated, so it is a valid repository name as it stands), or set package_name.

Packaging an instance that was never created, or one whose container is gone, is refused by name. The second is worth catching: docker commit reports it as a bare Error response from daemon: No such container: <64 hex characters>, which names neither the instance nor what to do next.

doctor

-----> The doctor is in
       Docker daemon at unix:///var/run/docker.sock is reachable, running 29.7.2.

Checks the daemon is reachable (and reports its version), that a configured tls_cacert / tls_cert / tls_key / dockerfile names a path that exists, and that a container named in the state file is still there.

Every check runs and the results are OR-ed rather than returning at the first problem — kitchen doctor exists to report the whole list at once. A true return is how Test Kitchen decides to exit non-zero.

status

Instance             Driver  ... Last Action  Last Error  Live Status
default-ubuntu-2404  Docker  ... Converged    <None>      running

running, stopped, gone (state names a container the daemon does not have), or not created — from the same two questions create and destroy already ask. An instance with no container is answered without touching Docker.

Not implemented

cache_directory, the fourth seam. It exists so a driver can hand the provisioner a host path to reuse between runs; this driver has no such path to offer, since everything lives inside the image and the container. Left inherited deliberately.

Confirmation

Docker 29.7.2 (Docker Desktop 4.87.0, macOS/arm64), Test Kitchen 4.1.1, real ubuntu-24.04 containers. Every block above is captured from a real run. Also checked:

• the packaged image runs — docker run --rm default-ubuntu-2404:latest cat /etc/os-release → Ubuntu 24.04.4 LTS
• --live distinguishes all four states: stopped the container → stopped; docker rm -f behind Kitchen's back → gone
• kitchen doctor exits 1 with a stale state file and 0 when healthy
• package on a removed container → Cannot package default-ubuntu-2404: the state file names container c94251d1..., which the daemon does not have. Run \kitchen destroy` to clear it.`
• ordinary converge / destroy unaffected

rake style clean; markdownlint clean; rspec 332 examples, 0 failures (19 new).