Subscribe to systemd on startup

Added code for the implementation of the method
subscribeToSystemdSignals. The reason for this is
because we want to catch the obmc-standby.target
signal and be notified when it is done which means
the BMC is READY.

Change-Id: I824b83676db8cb211f5bee954f98a719a773a62b
Signed-off-by: Josh D. King <jdking@us.ibm.com>
diff --git a/bmc_state_manager.hpp b/bmc_state_manager.hpp
index 6b1f62d..be88ba8 100644
--- a/bmc_state_manager.hpp
+++ b/bmc_state_manager.hpp
@@ -29,7 +29,27 @@
             const char* objPath) :
                 sdbusplus::server::object::object<
                     sdbusplus::xyz::openbmc_project::State::server::BMC>(
-                        bus, objPath) {};
+                        bus, objPath),
+                        bus(bus)
+        {
+            subscribeToSystemdSignals();
+        };
+
+        /** @brief Set value of BMCTransition **/
+        Transition requestedBMCTransition(Transition value) override;
+
+        /** @breif Set value of CurrentBMCState **/
+        BMCState currentBMCState(BMCState value) override;
+
+    private:
+        /**
+         * @brief subscribe to the systemd signals
+         **/
+        void subscribeToSystemdSignals();
+
+        /** @brief Persistent sdbusplus DBus bus connection. **/
+        sdbusplus::bus::bus& bus;
+
 
 };