RMS: Delete user data snapshots when deleting a rollback

- PackageRollbackInfo now also stores list of users the package is
  installed for and the inodes of backup CE data snapshot.
- Changed snapshotAppData to return a pair of
  <pendingBackups, ceSnapshotInodes>.
- RollbackData is updated with CE user data snapshot inode after user
  unlocks the phone and snapshotAppData call is made.
- Added javadoc to some methods in Installer.java to make lint happy.

Not sure how to automatically test:
- multi-user flow.
- the fact that user data snapshots were deleted. I can't access folder
  with snapshot data in RollbackTest, because it is owned by installd.

Bug: 112431924
Test: AppDataRollbackHelperTest, RollbackTest
Change-Id: Ife15f1aed9cf1d2b15be238bdaf766c51b85cab6