API Review: Return status code for user management APIs

- Replaced boolean return value with error code

Bug: 71866621
Test: com.android.cts.devicepolicy.DeviceOwnerTest#testCreateAndManageUser_StartInBackground
Test: com.android.cts.devicepolicy.DeviceOwnerTest#testCreateAndManageUser_StartInBackground_MaxRunningUsers
Test: com.android.cts.devicepolicy.DeviceOwnerTest#testCreateAndManageUser_CannotStopCurrentUser
Test: com.android.cts.devicepolicy.DeviceOwnerTest#testCreateAndManageUser_StopUser
Test: com.android.cts.devicepolicy.DeviceOwnerTest#testCreateAndManageUser_LogoutUser
Test: com.android.cts.devicepolicy.DeviceOwnerPlusProfileOwnerTest#testCannotStartManagedProfileInBackground
Test: com.android.cts.devicepolicy.DeviceOwnerPlusProfileOwnerTest#testCannotStopManagedProfile
Test: com.android.cts.devicepolicy.DeviceOwnerPlusProfileOwnerTest#testCannotLogoutManagedProfile
Change-Id: Iddc3e33c91c3f9584d53e537dbab3f61b8772fb1