extension: use map in create extension

Adjust the Create extension to use a map for metadata instead of
vector.

Tested: Unit tests updated and passing.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I9bd62b8dcc8b18a61958ed64de98b52a48333637
diff --git a/test/openpower-pels/additional_data_test.cpp b/test/openpower-pels/additional_data_test.cpp
index c93fdf2..45e1776 100644
--- a/test/openpower-pels/additional_data_test.cpp
+++ b/test/openpower-pels/additional_data_test.cpp
@@ -21,8 +21,8 @@
 
 TEST(AdditionalDataTest, GetKeywords)
 {
-    std::vector<std::string> data{"KEY1=VALUE1", "KEY2=VALUE2",
-                                  "KEY3=", "HELLOWORLD", "=VALUE5"};
+    std::map<std::string, std::string> data{
+        {"KEY1", "VALUE1"}, {"KEY2", "VALUE2"}, {"KEY3", ""}};
     AdditionalData ad{data};
 
     EXPECT_TRUE(ad.getValue("KEY1"));