Move start and stop of sub-systems to Trampoline

From BMS. Moved mUserServices list creation from BMS to Trampoline.
BMS still uses it but the plan is to move gradually in multiple
CLs to eventually delete it. Both are dealing with the same instance
because of this. Start and stop of sub-system (uBMS) is now handled in
Trampoline. getUserServices() was also moved. BMS robolectric tests were moved
to Trampoline *robolectric* tests to simplify this CL. After we merge BMS and
Trampoline, we can look into moving tests away from Robolectric.

Test: atest BackupManagerServiceTest TrampolineRoboTest TrampolineTest
Bug: 135661048
Change-Id: I4e612d06fe006c12f215a94f210450a5e6316b75