[Multi-user] Change BackupManager AIDL to accept userId in methods

Bug: 120120742

Test: 1) atest RunFrameworksServicesRoboTests
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
7) Toggle Backup/'Backup Now' in Settings
8) 'adb shell bmgr' enabled/backupnow flow

Change-Id: I5dba38f6a24e07947d1b0948f9caefeca011205d