[SPARK-18900][FLAKY-TEST] StateStoreSuite.maintenance

## What changes were proposed in this pull request?

It was pretty flaky before 10 days ago.
https://spark-tests.appspot.com/test-details?suite_name=org.apache.spark.sql.execution.streaming.state.StateStoreSuite&test_name=maintenance

Since no code changes went into this code path to not be so flaky, I'm just increasing the timeouts such that load related flakiness shouldn't be a problem. As you may see from the testing, I haven't been able to reproduce it.

## How was this patch tested?

2000 retries 5 times

Author: Burak Yavuz <brkyvz@gmail.com>

Closes #16314 from brkyvz/maint-flaky.