UserLifecycleStressTest: not stop user on switch

For devices with fw.stop_bg_users_on_switch=1, user will be stopped on
switch. This would cause the test itself to be killed, when the running
user is stopped.

This CL would prevent stop user on switch, by calling setStopUserOnSwitch,
which has higher priority.

Bug: 408273239
Flag: TEST_ONLY
Test: atest FrameworksServicesTests:com.android.server.pm.UserLifecycleStressTest will not crash on device with fw.stop_bg_users_on_switch=1
Change-Id: Id363f105354768a2c500914455ec1496df84abaf