Fix broken dexopt logic.

The logic was incorrect in the presence of multiple paths
(cluster installs) or multiple instruction sets (multi arch)
because of an early return in the case of sucessful dexopt.

- Rewrite this logic to make it (hopefully) clearer.
- Fix a related bug in getAppDexInstructionSets.
- Add instruction set to the dexopt logs.

bug: 16013931
Change-Id: I18c9755583f0a6f8be70469ec2062269564f0f41