HDDS-10217. Speed up TestKeyDeletingService

[adoroszlai]

What changes were proposed in this pull request?

Speed up TestKeyDeletingService:

[INFO] Tests run: 8, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 162.082 s - in org.apache.hadoop.ozone.om.service.TestKeyDeletingService

1. Start OM in per-class setup methods instead of per-test. Tests are moved into two nested classes, because some of them test normal operations, others simulate failing block delete requests. Most assertions had to be changed to not assume "empty" OM DB, similarly to HDDS-10215. Speed up some tests that use OmTestManagers #6107.
2. Reduce some service intervals.
3. Extract some helper methods.

https://issues.apache.org/jira/browse/HDDS-10217

How was this patch tested?

Total time is reduced to 40-45 seconds:

[INFO] Running org.apache.hadoop.ozone.om.service.TestKeyDeletingService
[INFO] Running org.apache.hadoop.ozone.om.service.TestKeyDeletingService$Failing
[INFO] Tests run: 3, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 16.812 s - in org.apache.hadoop.ozone.om.service.TestKeyDeletingService$Failing
[INFO] Running org.apache.hadoop.ozone.om.service.TestKeyDeletingService$Normal
[INFO] Tests run: 5, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 22.254 s - in org.apache.hadoop.ozone.om.service.TestKeyDeletingService$Normal
[INFO] Tests run: 0, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 39.151 s - in org.apache.hadoop.ozone.om.service.TestKeyDeletingService

CI:
https://github.com/adoroszlai/ozone/actions/runs/7729212630

Passed in 200 runs:
https://github.com/adoroszlai/ozone/actions/runs/7755051816

[smengcl]

Thanks @adoroszlai for refactoring this!

[adoroszlai]

Thanks @smengcl for the review.