PEL: Use the real system names property

There is now a 'Names' property on the new
xyz.openbmc_project.Configuration.IBMCompatibleSystem interface that the
DataInterface::getSystemNames function will read.  The existing code was
mostly a placeholder until the actual interface showed up on D-Bus.

Since the path that holds the interface is system specific, and the PEL
code should only rarely need this, the code was changed to read it on
demand instead of at caching it startup.

Since getSystemNames() no longer returns a cached value, the signature
was changed slightly to remove the reference from the returned
std::vector<std::string> value.

The UserHeader constructor used to make a call to getSystemNames every
time, and that was changed to only call it when actually necessary,
which is when there is a severity value defined in the message registry
that depends on the system name.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I1d4f307ef38287b631f94dae2b8929307d129029
diff --git a/extensions/openpower-pels/data_interface.hpp b/extensions/openpower-pels/data_interface.hpp
index 09bcf59..9a48721 100644
--- a/extensions/openpower-pels/data_interface.hpp
+++ b/extensions/openpower-pels/data_interface.hpp
@@ -239,10 +239,7 @@
      *
      * @return std::vector<std::string> - The list of names
      */
-    virtual const std::vector<std::string>& getSystemNames() const
-    {
-        return _systemNames;
-    }
+    virtual std::vector<std::string> getSystemNames() const = 0;
 
     /**
      * @brief Fills in the placeholder 'Ufcs' in the passed in location
@@ -401,11 +398,6 @@
      * @brief The motherboard CCIN
      */
     std::string _motherboardCCIN;
-
-    /**
-     * @brief The compatible system names array
-     */
-    std::vector<std::string> _systemNames;
 };
 
 /**
@@ -492,6 +484,13 @@
         getLocationCode(const std::string& inventoryPath) const override;
 
     /**
+     * @brief Get the list of system type names the system is called.
+     *
+     * @return std::vector<std::string> - The list of names
+     */
+    std::vector<std::string> getSystemNames() const override;
+
+    /**
      * @brief Fills in the placeholder 'Ufcs' in the passed in location
      *        code with the machine feature code and serial number, which
      *        is needed to create a valid location code.