Clear task in AllAppPermissionsFragmentTest

In order to truely clear the activity in between tests, the test must be
started with the CLEAR_TASK flag. Also, no need to wait 20 seconds for
the tests that are testing for lack of presence

Fixes: 267819179
Test: atest AllAppPermissionsFragmentTest
Change-Id: I4a723e1f411ed49c81de68ff6a7743a754176442