[Multi-user] Verfiy full backup/restore flow

Bug: 121198030
Test: 1) atest RunBackupFrameworksServicesRoboTests
2) atest $(find \
frameworks/base/services/tests/servicestests/src/com/android/server/backup \
-name '*Test.java')
3) atest CtsBackupTestCases
4) atest CtsBackupHostTestCases
5) atest GtsBackupTestCases
6) atest GtsBackupHostTestCases

Manual testing:
1. Start secondary user -> verify fb-schedule file is created, full backup queue initialised
2. Verify fullbackup of 1 package for system/secondary users, [package] only exists for current user:
  * bmgr --user [user-id] fullbackup [package]
  * Verify in logs that backup is successful
  * Uninstall/install [package]
  * Verify data is restored
3. Verify fullbackup of 1 package for secondary user, [package] eixtst for user 0:
  * bmgr fullbackup [package]
  * bmgr --user [user-id] fullbackup [package]
  * Verify in logs that backup is successful
  * Uninstall/install [package] for secondary user
  * bmgr --user [user-id] restore [token] [package]
  * Verify the data restored is different from system user data and belongs to [user-id]
3. Verify backup of all packages for system/secondary users:
  * bmgr --user [user-id] backupnow --all
  * Verify system packages (android, settings, wallpaper) are skipped for secondary user
  * Verify in logs that backup is successful
  * Uninstall/install [package]
  * Verify data is restored

Base -> Patchset 2: Update method calls to use asUser versions
Patchset 2 -> Patchset 3: Update opComplete callback to accept userId
Patchset 3 -> Patchset 4: Gate system packages from backup/restore for non-system users

Change-Id: Ic3986709ba4d46c0af9da45bb4dd682ee2aef3ce