audio: several concurrent capture fixes

Make sure AudioRecord clients are invalidated synchronously
when closing an input stream instead of when the capture thread
exits.

Fix AudioPolicyManager::getInputForDevice() logic to make sure that
not only the first opened input encountered is considered when looking
for a compatible input to reuse for concurrent capture.

Bug: 22702906
Test: run CTS test
Change-Id: I7f69609d4ee70a37ab06753ff970b12df17d885b