Client issue on command failure

[creack]

When the command fails directly, the client gets lost:
2014/03/25 16:27:25 Unrecognized input header

FROM ubuntu
RUN apt-get update && apt-get install docker

Reproduce:
docker run creack/segv docker (pushed on public registry)

/cc @vieux

[shykes]

I agree with this as an immediate solution.. I prefer moving away from "magical merging"
based on the commands you ran before. I think it's cleaner to unify the build interface,
so that you can explicitly tell Docker "please modify the image metadata in this or that way".
That's consistent with my docker commit --change PR for example.

Longer term, it would be nice to have a TTY build instruction to specify "the default entrypoint
should have a tty allocated". There are 2 caveats there:

1. Note that TTY should apply to the entrypoint, and not apply if the entrypoint is changed
   (either at run time or by an overlay image). It makes sense to say "by default run bash with a tty",
   but it doesn't make sense to say "whatever command you run in this container, always allocate a tty".

2. TTY is complicated to implement because it requires cooperation by the client, unlike most
   other build instructions. I am not sure how that work, but I have a feeling it's complicated :)

I will leave this long-term discussion for later.

[shykes]

@vieux could you move the test from integration to integration-cli? It should make it
even simpler :)

After that I think we can merge.

Sorry for the slow review.

[vieux]

@shykes what test ?

[shykes]

@vieux sorry about that, those 2 comments were meant to be posted on #4882. I re-posted them in the right place.