crit-service: add failed unit to error log

Whether it's a systemd target or a service, they are both units. Log
that unit name to both error logs so it's easy to tell what failed.

Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: I32fc45ece1e9ca9b986ead3c9675cf71857b7fcd
diff --git a/systemd_target_signal.cpp b/systemd_target_signal.cpp
index 9f778d5..c44e52f 100644
--- a/systemd_target_signal.cpp
+++ b/systemd_target_signal.cpp
@@ -20,7 +20,8 @@
 using sdbusplus::xyz::openbmc_project::Common::Error::InternalFailure;
 
 void SystemdTargetLogging::logError(const std::string& errorLog,
-                                    const std::string& result)
+                                    const std::string& result,
+                                    const std::string& unit)
 {
     auto method = this->bus.new_method_call(
         "xyz.openbmc_project.Logging", "/xyz/openbmc_project/logging",
@@ -28,8 +29,9 @@
     // Signature is ssa{ss}
     method.append(errorLog);
     method.append("xyz.openbmc_project.Logging.Entry.Level.Critical");
-    method.append(std::array<std::pair<std::string, std::string>, 1>(
-        {std::pair<std::string, std::string>({"SYSTEMD_RESULT", result})}));
+    method.append(std::array<std::pair<std::string, std::string>, 2>(
+        {std::pair<std::string, std::string>({"SYSTEMD_RESULT", result}),
+         std::pair<std::string, std::string>({"SYSTEMD_UNIT", unit})}));
     try
     {
         this->bus.call_noreply(method);
@@ -94,7 +96,7 @@
         // If this is a monitored error then log it
         if (!error.empty())
         {
-            logError(error, result);
+            logError(error, result, unit);
         }
     }
     return;
diff --git a/systemd_target_signal.hpp b/systemd_target_signal.hpp
index 8674ca5..c46425a 100644
--- a/systemd_target_signal.hpp
+++ b/systemd_target_signal.hpp
@@ -76,8 +76,10 @@
      *
      * @param[in]  error      - The error to log
      * @param[in]  result     - The failure code from the systemd unit
+     * @param[in]  unit       - The name of the failed unit
      */
-    void logError(const std::string& error, const std::string& result);
+    void logError(const std::string& error, const std::string& result,
+                  const std::string& unit);
 
     /** @brief Check if systemd state change is one to monitor
      *