js_container / js_container - invalid RC on failure

[jgebal]

When running js_container from shell script I'd like to be able to intercept return code.
This is however not working correctly today because the sys.exit(1) used in thread is not propagated to parent (main process).

As a result, if any of actions taken on any of containers fails, the script outputs Error ... but the return code is 0.

So when scripting with examples - we can't handle exceptions.