control: Add interfacesAdded signal support

Subscribe to and handle interfacesAdded signals to trigger event
actions.

Change-Id: I9d42a4341cb2880cf839b626786c569bdbf19a7c
Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
diff --git a/control/json/triggers/signal.hpp b/control/json/triggers/signal.hpp
index 1077144..32a9021 100644
--- a/control/json/triggers/signal.hpp
+++ b/control/json/triggers/signal.hpp
@@ -51,13 +51,24 @@
 void propertiesChanged(Manager* mgr, const std::string& eventName,
                        std::unique_ptr<ActionBase>& action);
 
+/**
+ * @brief Subscribes to an interfacesAdded signal
+ *
+ * @param[in] mgr - Pointer to manager of the trigger
+ * @param[in] eventName - Name of event associated to the signal
+ * @param[in] action - Action to be run when signal is received
+ */
+void interfacesAdded(Manager* mgr, const std::string& eventName,
+                     std::unique_ptr<ActionBase>& action);
+
 // Match setup function for signals
 using SignalMatch = std::function<void(Manager*, const std::string&,
                                        std::unique_ptr<ActionBase>& action)>;
 
 /* Supported signals to their corresponding match setup functions */
 static const std::unordered_map<std::string, SignalMatch> signals = {
-    {"properties_changed", propertiesChanged}};
+    {"properties_changed", propertiesChanged},
+    {"interfaces_added", interfacesAdded}};
 
 /**
  * @brief Trigger to process an event after a signal is received