improve feedback when repo2docker pod is killed

[minrk]

Bug description

When a build fails because a pod was deleted/killed/evicted/other kubernetes event, the end-user gets no messages about this

How to reproduce

1. launch a build
2. kill the build manually, or rely on kubernetes by exceeding resource limits
3. watch for feedback

Expected behaviour

Informative feedback about the failure

Actual behaviour

No feedback in the terminal, but progress bar reaches 'failed'.