Use a broadcast barrier in permissionpolicy

By running 'am wait-for-broadcast-barrier' before our test suite starts,
we ensure no broadcasts are pending. This prevents receiving old
broadcasts, and also can prevent timeouts by ensuring the broadcast
queue is empty before the test runs.

Bug: 341792090
Test: presubmit
Merged-In: I21fa03960e62fc3e8237a918f59ebcd61893f669
Change-Id: I21fa03960e62fc3e8237a918f59ebcd61893f669
1 file changed