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_interface.h b/supplicant_interface_proxy_interface.h
index e87d6ea..6788976 100644
--- a/supplicant_interface_proxy_interface.h
+++ b/supplicant_interface_proxy_interface.h
@@ -20,6 +20,7 @@
 
   virtual ::DBus::Path AddNetwork(
       const std::map<std::string, ::DBus::Variant> &args) = 0;
+  virtual void Disconnect() = 0;
   virtual void FlushBSS(const uint32_t &age) = 0;
   virtual void RemoveAllNetworks() = 0;
   virtual void RemoveNetwork(const ::DBus::Path &network) = 0;