Wait for the user to fully stop before starting

When starting the user, if the previous state is SHUTDOWN,
we need for the user to fully stop to avoid various race conditions like
old processes not being killed etc.

Test: manual - adb shell am start-user/stop-user N
Bug: 78533470
Change-Id: I1a188cc7c7f1f3df5c5448e67e811aba7d9d3b8e