Fix VPN profile path in settings.

http://b/issue?id=2485656

...and eliminate multiple Settings instances in history stack

Change-Id: I076b78781ee7ce458f82e6d9659a94ce64841a0e
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index 80c9766..97fbaec 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -189,7 +189,7 @@
 
         <activity android:name=".vpn.VpnSettings"
                 android:configChanges="orientation|keyboardHidden"
-                android:launchMode="singleTask">
+                android:clearTaskOnLaunch="true">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
                 <action android:name="android.net.vpn.SETTINGS" />