rai has a 0 exit status on an error

[cwpearson]

I submitted a rai job with the following build file

rai:
  version: 0.2
resources:
  cpu:
    architecture: ppc64le
  network: true
commands:
  build_image:
    image_name: raiproject/scope:ppc64le-cuda80-latest
    dockerfile: "./ppc64le.cuda80.Dockerfile"
    no_cache: true

The server provides the following output

[ 2018-08-14 14:53:27.533701863 +0000 UTC] ✱ Downloading your code.
[ 2018-08-14 14:53:47.104687599 +0000 UTC] ✱ Docker image name cannot start with rai/ . Choose a different prefix.
[ 2018-08-14 14:53:47.17477052 +0000 UTC] ✱ Unable to create image raiproject/scope:ppc64le-cuda92-latest.

I think in this case, the client should exit with a non-zero exit status.

[cwpearson]

I think if the client package returns an error when the execution fails, we will get a non-zero exit. Perhaps a new kind of client error could be created that refers to a non-zero job exit.