Fix a few issues with 616-cha-unloading.

- Disable test on RI
- Disable test on trace
- Don't try N times for getting the allocation we want, do it
  until we get it. We shouldn't get in an infinite loop. If
  we do the harness will kill the test.

Test: 616-cha-unloading
bug: 73143991

(cherry picked from commit a3cd1241)

Change-Id: I8d37dbcde472b19f63c7c692acea9e7d90f17d25