shill: implement Service.Disconnect (for WiFiService only)

BUG=chromium-os:23774,chromium-os:23662
TEST=new unit tests, some autotests

autotests run:
- PASS network_WiFiSecMat.031CheckHidden_WPA
- PASS network_WiFiSecMat.032CheckHidden_RSN

Change-Id: I0c2dc8c9888caca793f0dfe5a55c0df2a4b10c79
Reviewed-on: https://gerrit.chromium.org/gerrit/12498
Commit-Ready: mukesh agrawal <quiche@chromium.org>
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Tested-by: mukesh agrawal <quiche@chromium.org>
diff --git a/supplicant_interface_proxy.h b/supplicant_interface_proxy.h
index 82d3a1c..1bc5546 100644
--- a/supplicant_interface_proxy.h
+++ b/supplicant_interface_proxy.h
@@ -29,6 +29,7 @@
 
   virtual ::DBus::Path AddNetwork(
       const std::map<std::string, ::DBus::Variant> &args);
+  virtual void Disconnect();
   virtual void FlushBSS(const uint32_t &age);
   virtual void RemoveAllNetworks();
   virtual void RemoveNetwork(const ::DBus::Path &network);