Fix KeyguardTests#testScreenOffCausesSingleStopAod

When the devices goes into doze mode to display AOD contents, the screen
turns off before displaying AOD contents on some devices (i.e.
config_displayBlanksAfterDoze=true).

On such devices, SysUI calls IActivityTaskManager#setLockScreenShown
first before start dozing, otherwise ATMS/WM wakes up the activities
when dozing starts.

Bug: 193479273
Test: manual
  1. adb root && adb shell setprop debug.force_blanking 1 && adb reboot
  2. atest KeyguardTests
Change-Id: I64cecd8e866f1debdcd7429ca4987cd70eceb45c