- What I did
Added an option to customize containerd service name which is a dependency for docker. This is required in case we need to run several instances of docker along with dedicated instance of containerd service.

- How I did it
Added and extra config variable CONTAINERD_SVC. Existing behavior preserved by using respective default.

- How to verify it
On Gentoo use this fix for containerd.

1. Create separate containerd and docker services:

ln -rs /etc/init.d/containerd{,-test}
ln -rs /etc/init.d/docker{,-test}

2. Configure containerd service by creating /etc/conf.d/containerd-test with content:

containerd_socket_address="/run/containerd-test/containerd-test.sock"
command_args="--root=/var/lib/containerd-test --state=/run/containerd-test --address=${containerd_socket_address:-/run/containerd/containerd.sock}"

3. Configure docker service by creating /etc/conf.d/docker-test with content:

CONTAINERD_SVC="containerd-test"
DOCKER_OPTS="--data-root=/var/lib/docker-test --exec-root=/var/run/docker-test --host=unix:///var/run/docker-test.sock --containerd=/run/containerd-test/containerd-test.sock"

4. Start docker:

/etc/init.d/docker-test start

Expected result:
Respective containerd-test service should start up automatically.
Both containerd-test and docker-test services should work in parallel with standard containerd and docker services.

- Human readable description for the release notes

Allow customizing containerd service name for OpenRC

- A picture of a cute animal (not mandatory but encouraged)