[SPARK-20358][CORE] Executors failing stage on interrupted exception thrown by cancelled tasks

## What changes were proposed in this pull request?

This was a regression introduced by my earlier PR here: https://github.com/apache/spark/pull/17531

It turns out NonFatal() does not in fact catch InterruptedException.

## How was this patch tested?

Extended cancellation unit test coverage. The first test fails before this patch.

cc JoshRosen mridulm

Author: Eric Liang <ekl@databricks.com>

Closes #17659 from ericl/spark-20358.