Fix process capabilities on re-computation for cycles in oomAdjuster

When retrying the oomAdj computation because of cycles, it's scanning
the list of processes in the opposite direction, we should preserve
whatever capabilities we have got before the retry.

Bug: 206585758
Test: atest MockingOomAdjusterTests
Change-Id: Ia7d0ec7a39aac5bf59ae837b4af1ed7b6512521c
Merged-In: Ia7d0ec7a39aac5bf59ae837b4af1ed7b6512521c