Implement AvahiMdnsClient

Implement the AvahiMdnsClient interface.  This is based on code
from peerd/avahi_client.cc and avahi_service_publisher.cc.

Bug: 23288773
Change-Id: If58df0bf3d71c665c764ca8994b43dcff237549e
diff --git a/buffet/webserv_client.cc b/buffet/webserv_client.cc
index 2ae5910..37c9716 100644
--- a/buffet/webserv_client.cc
+++ b/buffet/webserv_client.cc
@@ -84,7 +84,7 @@
       base::Bind(&WebServClient::OnProtocolHandlerDisconnected,
                  weak_ptr_factory_.GetWeakPtr()));
 
-  web_server_->Connect(bus, buffet::kServiceName,
+  web_server_->Connect(bus, buffet::dbus_constants::kServiceName,
                        sequencer->GetHandler("Server::Connect failed.", true),
                        base::Bind(&base::DoNothing),
                        base::Bind(&base::DoNothing));