diagnostics should default to an embedded hello-world docker image
The diagnostics run a test container to verify that crunch is working. However, it assumes that an
alpine image (or a different image specified on the command line, perhaps
arvados/jobs:latest) has been loaded. Our install process doesn't load any images, because arvados-cwl-runner is responsible for loading the image that corresponds to the exact version of a-c-r being used, on demand.
Running the "/hello" command with the "hello-world" image would work just as well, and that image is only ~20KB.
The diagnostics command should embed the hello-world image, and upload it to Keep at runtime, instead of relying on the docker daemon being installed/working on the client host.
Continue to support the
-docker-image=... option as well (assume the image is already uploaded).
Requested command should be
/hello if using the
hello-world image, otherwise