Change ToolBar default icon on the left

Question

I am using a ToolBar at the top at present and want to replace the default back button with a home button. But when I add item, it always adds to the right. I don't see any layout_gravity options to choose either. Is there a way to do this?

MainActivity

Toolbar toolbar;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_add_delete);

    toolbar = (Toolbar)findViewById(R.id.app_bar);
    setSupportActionBar(toolbar);
    getSupportActionBar().setTitle("                Testing");
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.home_icon_empty, menu);
    return true;
}

home_icon_empty.xml

<item
    android:id="@+id/homepage"
    android:orderInCategory="100"
    android:title="HOME"
    android:icon="@drawable/home_icon"
    app:showAsAction="always"
    />

<item
    android:id="@+id/homepage1"
    android:orderInCategory="200"
    android:title="HOME"
    android:icon="@drawable/home_icon"
    app:showAsAction="always"
    />

activity_main.xml

<include
        android:id="@+id/app_bar"
        layout="@layout/app_bar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

app_bar.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.Toolbar xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@color/colorPrimary">

</android.support.v7.widget.Toolbar>

Current Toolbar output:

Expected Toolbar output:

Image after new edit:

Answer 1

Set as NavigationIcon:

Drawable drawable = ContextCompat.getDrawable(context, R.drawable.your_drawable)
toolbar.setNavigationIcon(drawable);
setSupportActionBar(toolbar);