Fix logging

Summary: Refactor logging. want to log the substituted values for mcrouter config read with luna with the existing value

Reviewed By: disylh

Differential Revision: D73125655

fbshipit-source-id: b62b1ccd0d251ea8939f5a1a23e8ebc6de67d261

Author: Abhi Sengupta

third-party/mcrouter/src/mcrouter/options.cpp

@@ -278,7 +278,7 @@ vector<McrouterOptionMismatch> McrouterOptionsBase::compare(
           McrouterOptionMismatch e;
           e.optionName = name;
           e.lunaValue = it->second;
-          e.errorMsg = "luna value " + it->second +
+          e.errorMsg = "luna value " + subValue +
               " and current mcrouter_options value " + currValue +
               " are different";
           errors.push_back(std::move(e));