Add callback support to triggerable actions

Change-Id: Icc27fbe9403eda418f41e12c76af7f3216f4b72a
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/bmc/general_systemd.cpp b/bmc/general_systemd.cpp
index 3c59c11..ecd15d4 100644
--- a/bmc/general_systemd.cpp
+++ b/bmc/general_systemd.cpp
@@ -144,6 +144,11 @@
     job = std::nullopt;
     currentStatus =
         result == "done" ? ActionStatus::success : ActionStatus::failed;
+
+    if (cb)
+    {
+        cb(*this);
+    }
 }
 
 std::unique_ptr<TriggerableActionInterface>