Merge changes Ib05902aa,Id7e8efaa,I3408af12,I6cc3b276,I9c94d2f5, ...

* changes:
  Add support for rollback of multiPackage installs.
  Add multi-package support to RollbackData.
  RollbackManagerService: Add getRollbackForPackage helper function.
  Reorganize rollback data storage layout.
  Rename PackageRollbackData RollbackData.
  Make rollbacks available only after session commit.