Add bottom padding of profile group on Bluetooth detail page

- This CL add a bottom padding preference to make UI consistency.
- Update test case

Bug: 146522686
Test: make -j42 RunSettingsRoboTests
Change-Id: I525d8a3b71535972755de92924a3c04768f68e63

res/layout/preference_bluetooth_profile_category.xml

@@ -0,0 +1,26 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  Copyright (C) 2020 The Android Open Source Project
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+  -->
+
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+              android:layout_width="match_parent"
+              android:layout_height="wrap_content"
+              android:gravity="center_vertical"
+              android:orientation="horizontal"
+              android:paddingStart="?android:attr/listPreferredItemPaddingStart"
+              android:paddingTop="16dp"
+              android:paddingEnd="?android:attr/listPreferredItemPaddingEnd">
+</LinearLayout>