Pipelines build hangs if invalid auth given for build image.

If I create a pipeline which uses a private Docker image, but I provide incorrect authentication to retrieve it, then my step will hang indefinitely (until it times out).

Example YAML:

#!yaml

image:
  name: phodder/private-image
  username: phodder
  password: wrongpassword
pipelines:
  default:
    - step:
        script:
          - echo "Hello world"

The first step will never leave the 'Pulling Images' state.