Fix flaky keyguard tests

- After entering password to unlock, the top activity
  may take some time to be visible.
- Window token may be removed later than activity record.

Bug: 117599433
Bug: 116680685
Test: atest KeyguardLockedTests#testDismissKeyguard_whileOccluded
Test: atest KeyguardTests#testUnoccludeRotationChange
Change-Id: Ie3b4b0a7328702f7cc80f8dac27fde25b6a015ea