kubernetes: Make pods/exec websocket channel 3 content easier to parse exit code

/kind feature

What happened:

As part of kubernetes-client/java, I’m looking at the websocket calls for pods/exec. When the exec’d process exits with a non-zero code, we would like to provide this exit code value to the caller.

Exec status information is provided through websocket channel 3; however, this content is presently unstructured. For instance, the following content was returned:

command terminated with non-zero exit code: Error executing in Docker Container: 1

What you expected to happen:

I’d like to see the status returned as a JSON object with an exitCode attribute.

How to reproduce it (as minimally and precisely as possible):

1. Create a Pod that has a script that returns a non-zero exit code.
2. kubectl exec this Pod and script and watch the traffic on channel 3.

Anything else we need to know?:

Environment:

• Kubernetes version (use kubectl version): Client Version: version.Info{Major:“1”, Minor:“9”, GitVersion:“v1.9.2”, GitCommit:“5fa2db2bd46ac79e5e00a4e6ed24191080aa463b”, GitTreeState:“clean”, BuildDate:“2018-01-18T10:09:24Z”, GoVersion:“go1.9.2”, Compiler:“gc”, Platform:“darwin/amd64”} Server Version: version.Info{Major:“1”, Minor:“8”, GitVersion:“v1.8.7”, GitCommit:“b30876a5539f09684ff9fde266fda10b37738c9c”, GitTreeState:“clean”, BuildDate:“2018-01-16T21:52:38Z”, GoVersion:“go1.8.3”, Compiler:“gc”, Platform:“linux/amd64”}
• Cloud provider or hardware configuration:
• OS (e.g. from /etc/os-release):
• Kernel (e.g. uname -a):
• Install tools:
• Others: