Ability to use dunner with docker images whose entrypoint is defined

For Docker images whose entrypoint is defined and are run as an executable, Dunner fails to execute commands defined in it.

Example: Goreleaser's docker file.

Dunner task file:

tasks:
  release:
    steps:
      - image: goreleaser/goreleaser
        commands:
          - ["echo", "hello"]
          - ["goreleaser", "--version"]

Running this command with dunner fails with error as:

OCI runtime exec failed: exec failed: cannot exec a container that has stopped: unknown
FATA[2019-08-26 18:39:51] docker: command execution failed with exit code 126

Start by reproducing the failure with Goreleaser's Dockerfile, the shown .dunner.yaml task, and Dunner do release. Trace how Dunner starts the image and executes its commands when an entrypoint is defined. Done means both echo hello and goreleaser --version run successfully in that image.