Attn: Cleanup trace messages

Remove occurrances of ss.str().c_str() and use std::string in lieu of
stringstream when stringstream conveniences are not needed.

Signed-off-by: Ben Tyner <ben.tyner@ibm.com>
Change-Id: Ie80a64a0d63eb4a24ef905c72b2dbe1390e9bacc
diff --git a/attn/attn_logging.cpp b/attn/attn_logging.cpp
index 70acaa4..c4ab877 100644
--- a/attn/attn_logging.cpp
+++ b/attn/attn_logging.cpp
@@ -129,9 +129,9 @@
         }
         catch (const std::exception& e)
         {
-            std::stringstream ss;
-            ss << "createFFDCFiles: " << e.what();
-            trace<level::INFO>(ss.str().c_str());
+            std::string traceMessage =
+                "createFFDCTraceFiles: " + std::string(e.what());
+            trace<level::INFO>(traceMessage.c_str());
         }
     }
 }