entry: use map for metadata in ctor

Transition the entry constructor to use the `map<string,string>`
rather than the `vector<string>`.

Tested: UTs pass and daemon still creates logs.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Icf3ead163cc99a1498734d33335fb6da52e6c98c
diff --git a/test/serialization_test_properties.cpp b/test/serialization_test_properties.cpp
index 60fc6ae..f769c93 100644
--- a/test/serialization_test_properties.cpp
+++ b/test/serialization_test_properties.cpp
@@ -13,7 +13,8 @@
 {
     auto id = 99;
     phosphor::logging::AssociationList assocations{};
-    std::vector<std::string> testData{"additional=1", "data=yes"};
+    std::map<std::string, std::string> testData = {{"additional", "1"},
+                                                   {"data", "yes"}};
     uint64_t timestamp{100};
     std::string message{"test error"};
     std::string fwLevel{"level42"};