Populate APK files using hard links (2/n)

This is an effort to improve the storage usage of RollbackManager.

When committing a rollback, the apk/apex files will be deleted after
the install session is committed successfully. We can use hard links
to effectively transfer the files to PackageInstaller to avoid copy.

Bug: 168562373
Test: atest RollbackTest StagedRollbackTest

Change-Id: I749a17d769d1845bb0f9b34c8757b69b40b516f9