PEL: Create registry directory for test

The PEL manager test wasn't creating the message registry
directory before writing into it, and seemed to have just
been lucking out that a previous test had created it.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I122242d65db02d8b80864c938cc28be434774304
diff --git a/test/openpower-pels/pel_manager_test.cpp b/test/openpower-pels/pel_manager_test.cpp
index 1d4d3b7..a84ea7a 100644
--- a/test/openpower-pels/pel_manager_test.cpp
+++ b/test/openpower-pels/pel_manager_test.cpp
@@ -114,7 +114,10 @@
 }
 )";
 
-    fs::path path = getMessageRegistryPath() / "message_registry.json";
+    auto path = getMessageRegistryPath();
+    fs::create_directories(path);
+    path /= "message_registry.json";
+
     std::ofstream registryFile{path};
     registryFile << registry;
     registryFile.close();