Spark runner should not used STOPPED state as a terminal state

Over at BEAM-8539 we're trying to iron out the definitions of the job state enums.  One thing that is clear is that STOPPED is not supposed to be a terminal state, though since it was poorly documented it slipped in a few places.

There are two places in the `SparkPipelineResult` where STOPPED seems to be used as a terminal event.   These should either be DONE, FAILED, or CANCELLED.

Here's one example:

[https://github.com/apache/beam/blob/master/runners/spark/src/main/java/org/apache/beam/runners/spark/SparkPipelineResult.java#L133](https://github.com/apache/beam/blob/master/runners/spark/src/main/java/org/apache/beam/runners/spark/SparkPipelineResult.java#L133)

Imported from Jira [BEAM-8552](https://issues.apache.org/jira/browse/BEAM-8552). Original Jira may contain additional context.
Reported by: chadrik.