Add Docker to services list in multinode CI environments

Add Docker to services list in multinode CI environments

We need the service to be present to run jobs involving containers. Note
that this is effectively a no-op for the current CI jobs, as by default
the Docker service is mapped to OS::Heat::None. Docker will actually be
deployed only if environments/docker.yaml is included in the deploy
command.

Change-Id: I97a35e30e428ff64feeb411bf63dbb7aa54f9829