Allow test to run on lockscreen

Test failed when on lockscreen which could be caused by other tests not
cleaning up properly or unrelated failures, so, add a flag to allow the
test activity to display on lockscreen and ensure power menu will close
afterwards (home key does not work on lockscreen)

Not totally sure this will solve the flakes (although it passes locally
when running with --rerun-until-failure), so also annotating for now

Bug: 176891566
Test: atest; verified passes if run when device locked
Change-Id: Ia4143d145c991edda481519be2d32afcab92dfd5