[SPARK-18373][SPARK-18529][SS][KAFKA] Make failOnDataLoss=false work with Spark jobs

## What changes were proposed in this pull request?

This PR adds `CachedKafkaConsumer.getAndIgnoreLostData` to handle corner cases of `failOnDataLoss=false`.

It also resolves [SPARK-18529](https://issues.apache.org/jira/browse/SPARK-18529) after refactoring codes: Timeout will throw a TimeoutException.

## How was this patch tested?

Because I cannot find any way to manually control the Kafka server to clean up logs, it's impossible to write unit tests for each corner case. Therefore, I just created `test("stress test for failOnDataLoss=false")` which should cover most of corner cases.

I also modified some existing tests to test for both `failOnDataLoss=false` and `failOnDataLoss=true` to make sure it doesn't break existing logic.

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #15820 from zsxwing/failOnDataLoss.