Copy step-runner binary to job Docker container

Problem

Job's define an image:, which is the image used to create the Docker container that runs the job. For step-runner to run in the container, the step-runner binary needs to be installed on the container.

Proposal

• Take the Docker image created from Release step runner binaries (#126 - closed) • Cameron Swords
• Pull the container appropriate for the intended platform
• Extract the binary found on the image
• Copy into the executing Docker container