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.cc b/supplicant_interface_proxy.cc
index bfeb9b9..ac182cf 100644
--- a/supplicant_interface_proxy.cc
+++ b/supplicant_interface_proxy.cc
@@ -31,6 +31,10 @@
   return proxy_.AddNetwork(args);
 }
 
+void SupplicantInterfaceProxy::Disconnect() {
+  return proxy_.Disconnect();
+}
+
 void SupplicantInterfaceProxy::FlushBSS(const uint32_t &age) {
   return proxy_.FlushBSS(age);
 }