PEL: Implement CreatePELWithFFDCFiles

This D-Bus method on the org.open_power.Logging.PEL interface is the
same as the already existing createWithFFDCFiles method on the
xyz.openbmc_project.Logging.Create interface, except it also returns the
IDs of the newly created OpenBMC event log and PEL.

Code was added to track the IDs of the most recently added event log and
PEL so they they can be returned by the function.

Change-Id: I3a1e0d93f97aa1953ff8b10293b47e28f79edfb1
diff --git a/test/openpower-pels/repository_test.cpp b/test/openpower-pels/repository_test.cpp
index 403245a..f1a4a31 100644
--- a/test/openpower-pels/repository_test.cpp
+++ b/test/openpower-pels/repository_test.cpp
@@ -85,6 +85,8 @@
     auto newData = readPELFile(file);
     auto pelData = pel->data();
     EXPECT_EQ(*newData, pelData);
+
+    EXPECT_EQ(repo.lastPelID(), pel->id());
 }
 
 TEST_F(RepositoryTest, RemoveTest)