nexus: Flesh out VPN support a bit more, cleanup service handling

Signed-off-by: San Mehat <san@google.com>
diff --git a/nexus/ErrorCode.h b/nexus/ErrorCode.h
index 8ca6cae..57c99c2 100644
--- a/nexus/ErrorCode.h
+++ b/nexus/ErrorCode.h
@@ -26,6 +26,9 @@
     static const int WifiScanResult = 125;
     static const int WifiNetworkList = 126;
 
+    static const int VariableRead = 127;
+    static const int VariableWrite = 128;
+
     // 200 series - Requested action has been successfully completed
     static const int CommandOkay = 200;