Function dockerImage_ensure

dockerImage_ensure(image: string, run?: DockerRun): Promise<string | null>
Makes sure an image is present locally, pulling it when it is not.
Parameters
- image: string
  The image reference.
- run: DockerRun = docker_run
  The docker seam.
Returns Promise<string | null>
Null when the image is present; else why it could not be had.
Example
```
await dockerImage_ensure('fnndsc/pl-dircopy:2.1.1'); // null
```
- Defined in salsa/src/plugins/plugin_docker.ts:97