Jenkins Swarm based executor Docker image

A basic Docker image that will connect to a Jenkins master using the Jenkins Swarm Plugin and includes a Docker client pre-installed.

For a simple example running on swarm, see the full-demo subdirectory here.

Example usage via docker-compose / stack YAML:

...
services:
  executor-node:
    image: ericsmalling/jenkins_executor
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
      - ./workspace:/var/jenkins_workspace
...