euphoria-flink: detached mode execution

[xitep]

Euphoria's flink executor relies on the environment.execute() to be a blocking call. However, if we submit a program in flink's detached mode on yarn, e.g. flink -d ..., the method call does not block, and the euphoria executor continues to immediately commit/close all data sinks making the submitted flows fail at some point in time.

We should be able to detect being run in detached mode using something a long the lines of environment.getBatchEnv/getStreamEnv() instanceof DetachedEnvironment. However, we don't have any possibility to hook in code after the execution of the job has finished (in order to commit the sinks.)

It seems like Apache Beam fought a similar problem. Though, they were lucky not to have any code to be executed strictly after the job finished.