audiomixerbin: Add test file

Change-Id: I50d9abc4e4c30d000824602221f29e9e70b6d9d1
audiomixerbin: Release resources when release pad is called

This matches better with gstreamer's philosophy

Change-Id: Ifa3584d11049e16d08f9d642dd86bab59ad96b0a
audiomixerbin: Drain off all buffers before releasing a pad in playing state

Change-Id: Id81d501080ff10ee5652226c620a76cdd39e0911
audiomixerbin: Remove elements when pad is released and it is not in playing state

Change-Id: Iceecc596c044497f414b95cc86cd7e0acf68fa19
audiomixerbin: Add disconnection tests

Change-Id: I06a01c4e39bf2752ced1362fe35bf94fbab91027
audiomixerbin: Release pads on disposing

Change-Id: Ib0dfdeec869f450b86dd1ec7521b888996a624ac