BT: Make Bluetooth HCI VTS tests more stable

Extend to 600 ms sleep after BluetoothHci->close() to give HAL an ample
time to shutdown

Test: make, VtsHalBluetoothV1_0TargetTest
Bug: 176503623
Change-Id: If6d293167309b9dbcae94cf03199a6c95ecf9836
1 file changed