PackageParser: Disable package cache on "eng" builds.

- Catch a wider variety of exceptions from the package parse
  stage. Ignore and delete the cache entry if we catch *any*
  exceptions from deserializing the parse result.

- Rename the system property pm.boot and not ro.boot, since the
  former needs less effort to change back and forth.

- Finally, add a heuristic to wipe caches on non-numbered
  userdebug builds when changes to the system partition are detected.

Also re-enable the cache by reverting commit
20274d15.

Test: Manual
Change-Id: I7b5b71ac60d8c438398c354be50b207e80550148