[SPARK-20957][SS][TESTS] Fix o.a.s.sql.streaming.StreamingQueryManagerSuite listing

## What changes were proposed in this pull request?

When stopping StreamingQuery, StreamExecution will set `streamDeathCause` then notify StreamingQueryManager to remove this query. So it's possible that when `q2.exception.isDefined` returns `true`, StreamingQueryManager's active list still has `q2`.

This PR just puts the checks into `eventually` to fix the flaky test.

## How was this patch tested?

Jenkins

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #18180 from zsxwing/SPARK-20957.