Increase Unit Tests for BluetoothPhoneServiceImpl

Adds tests to BluetoothPhoneServiceImpl in code areas
that have been identified as important (76% -> 86%) as per:

go/telecom-code-yellow-coverage

Change-Id: I1294f5873ea0944c79878797e244db346b2ad9a4
diff --git a/src/com/android/server/telecom/BluetoothPhoneServiceImpl.java b/src/com/android/server/telecom/BluetoothPhoneServiceImpl.java
index 17d4b30..5c7cae4 100644
--- a/src/com/android/server/telecom/BluetoothPhoneServiceImpl.java
+++ b/src/com/android/server/telecom/BluetoothPhoneServiceImpl.java
@@ -380,7 +380,8 @@
     /**
      * Receives events for global state changes of the bluetooth adapter.
      */
-    private final BroadcastReceiver mBluetoothAdapterReceiver = new BroadcastReceiver() {
+    @VisibleForTesting
+    public final BroadcastReceiver mBluetoothAdapterReceiver = new BroadcastReceiver() {
         @Override
         public void onReceive(Context context, Intent intent) {
             synchronized (mLock) {