HDDS-9954. Simplify assertions in hadoop-ozone unit tests

[adoroszlai]

What changes were proposed in this pull request?

Assertions in the form:

assertTrue(<x> == <y>)
assertEquals(null, <x>) or assertTrue(<x> == null)
assertTrue(<x> != null)
assertEquals(<boolean>, <x>)

can be simplified to:

assertEquals(<x>, <y>)
assertNull(<x>)
assertNotNull(<x>)
assertTrue/assertFalse(<x>)

Not only are these simpler, some of them also provide more information in case of failure.

This PR updates such assertions in hadoop-ozone (except integration tests).

https://issues.apache.org/jira/browse/HDDS-9954

How was this patch tested?

CI:
https://github.com/adoroszlai/ozone/actions/runs/7250386337

[hemantk-12]

Thanks @adoroszlai for the patch.

LGTM.

[adoroszlai]

Thanks @aswinshakil, @hemantk-12 for the review.