Fix bug 2578813 Delay pausing music and routing audio for car docks

Moved broadcast of ACTION_AUDIO_BECOMING_NOISY from BluetoothA2dpService
to AudioService.
Broadcast ACTION_AUDIO_BECOMING_NOISY when disconnecting an A2DP
device.
Disconnect from A2DP docks with a delay to handle transient
disconnections.
Cancel delayed A2DP disconnections when connecting to a dock as this
can be a reconnection after a transient disconnection.

Change-Id: I1ee9e99f3ffa20727af38a4c4c8711942894a696