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

This change makes all logging output BUFFERED

refs: #1440

Change-Id: Ief60c43b532e4524a70aad2bf15aa06490847535
diff --git a/daemon/core/logger.hpp b/daemon/core/logger.hpp
index e0241ff..0b545e0 100644
--- a/daemon/core/logger.hpp
+++ b/daemon/core/logger.hpp
@@ -135,7 +135,7 @@
 #define NFD_LOG(level, expression)                                      \
 do {                                                                    \
   if (g_logger.isEnabled(::nfd::LOG_##level))                           \
-    std::cerr << ::nfd::Logger::now() << " "#level": "                  \
+    std::clog << ::nfd::Logger::now() << " "#level": "                  \
               << "[" << g_logger << "] " << expression << "\n";         \
 } while (false)
 
@@ -148,13 +148,13 @@
 #define NFD_LOG_WARN(expression)                                        \
 do {                                                                    \
   if (g_logger.isEnabled(::nfd::LOG_WARN))                              \
-    std::cerr << ::nfd::Logger::now() << " WARNING: "                   \
+    std::clog << ::nfd::Logger::now() << " WARNING: "                   \
               << "[" << g_logger << "] " << expression << "\n";         \
 } while (false)
 
 #define NFD_LOG_FATAL(expression)                                       \
 do {                                                                    \
-  std::cerr << ::nfd::Logger::now() << " FATAL: "                       \
+  std::clog << ::nfd::Logger::now() << " FATAL: "                       \
             << "[" << g_logger << "] " << expression << "\n";           \
 } while (false)
 
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);
   }