Parse App errors from CloudExecutables that use sub-shell

[mrgrain]

Errors thrown by CDK Apps are just printed to stdout/stderr by the subprocess. we should intercept, capture and re-throw the error. Instead this should be thrown by toolkit.synth directly.

We need to pass a magic env variable CDK_SERIALIZE_ERRORS to the cdk app. When this variable is set, then we add the following snippet:

process.on('uncaughtException', function(err) {
  // do magic here, e.g.
  console.error('Caught exception: ' + err);
});

This needs to somehow announce to the parent process that the app is no sending a JSON serialized error through the channel.

In the CLI/Toolkit we need to detect this and NOT print regularly. Instead we deserialize the error, recreate it to a proper Node exception and re throw it (toolkit). In the CLI we can also add some nice formatting on the error.