OomAdjuster: skip persistent/system processes in cycle detection

Apps with negative oom_adj scores are either system_server or
persistent. As a result, those apps don't need to be considered in
cycle detection because no binding to that app can possibly promote
the persistent process to a more important process state.

Bug: 260854804
Test: atest MockingOomAdjusterTests

Change-Id: I632dc41a5660935b9c49af3c01243314dab4cc0a