core: change NFD_LOG_* macros to use std::clog

This change makes all logging output BUFFERED

refs: #1440

Change-Id: Ief60c43b532e4524a70aad2bf15aa06490847535
diff --git a/tests/core/logger.cpp b/tests/core/logger.cpp
index faff2a6..628c1ce 100644
--- a/tests/core/logger.cpp
+++ b/tests/core/logger.cpp
@@ -25,15 +25,15 @@
 {
 public:
   LoggerFixture()
-    : m_savedBuf(std::cerr.rdbuf())
+    : m_savedBuf(std::clog.rdbuf())
     , m_savedLevel(LoggerFactory::getInstance().getDefaultLevel())
   {
-    std::cerr.rdbuf(m_buffer.rdbuf());
+    std::clog.rdbuf(m_buffer.rdbuf());
   }
 
   ~LoggerFixture()
   {
-    std::cerr.rdbuf(m_savedBuf);
+    std::clog.rdbuf(m_savedBuf);
     LoggerFactory::getInstance().setDefaultLevel(m_savedLevel);
   }