[Multi-user] Transport changes

Bug: 121197942

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

Change-Id: If9c23a7d6b2fc936502d184f585041cf91ad5893