Wait for ACTION_MEDIA_MOUNTED before removing started users.

Removing users immediately after starting them was causing system
crashes on other parts of the Android.

This CL makes sure ACTION_MEDIA_MOUNTED broadcast is received for
those users (who received ACTION_USER_STARTED), before deleting them.

This CL achives that by introducing a BroadcastWaiter helper class and
does some code refactoring to move broadcast waiting related code from
UserLifecycleTests into BroadcastWaiter.

Bug: 233240023
Test: atest MultiUserPerfTests:android.multiuser.UserLifecycleTests --no-bazel-mode
Change-Id: Ic7f3bdcdc700ad24add30b72855914a64cf0dafe