Create a simple fallback activity to be started if no other activity could be
resolved when Add supervised user option is tapped in Multi User settings.
Bug: 207495450
Test: croot && make RunSettingsRoboTests -j40 ROBOTEST_FILTER="com.android.settings.users.UserSettingsTest"
Change-Id: I850a2798567787c2494c75aa5fa451ddf373410d