Plumbing in PackageManager and installd for multi-user support.

- Create /data/user directory and symlink /data/user/0 -> /data/data for
  backward compatibility
- Create data directories for all packages for new user

- Remove data directories when removing a user

- Create data directories for all users when a package is created

- Clear / Remove data for multiple users

- Fixed a bug in verifying the location of a system app

- pm commands for createUser and removeUser (will be disabled later)

- symlink duplicate lib directories to the original lib directory

Change-Id: Id9fdfcf0e62406a8896aa811314dfc08d5f6ed95