Fix CacheOomRankerTest.

These tests were using `assertThat(x).containsExactly(y)`, which does
not check for order. We need to append `.inOrder()`. This exposes a
couple of other issues in the tests (but fortunately none in the actual
code!).

Test: atest CacheOomRankerTest
Change-Id: I9facbdaf3b1fe7c91f5e387e7c44a9b1e9be2d6f