Frameworks/base: Extract packages after cache pruning

In case the runtime pruned the dalvik cache on boot, run the package
extraction logic, so we have working oat files.

As the system server only runs in the primary ABI, this is best effort
and won't hit if only the secondary ABI has been pruned.

Bug: 27618311
Change-Id: I178d18d731a9dce5cb11ed0874c9c9c9d36d7d8e