core: change logging from environment variable to configuration file-based

GlobalConfigurationFixture uses unit-tests.conf to determine default
and module specific logging levels. Logging will gracefully default to
INFO if unit-tests.conf is not found. See unit-tests.conf.sample for a
sample configuration file.

refs: #1375, #1267

Change-Id: Ib0c4eb4149748e6658f94ef1afa23ddd3072c0fa
diff --git a/daemon/fw/strategy.cpp b/daemon/fw/strategy.cpp
index d41786d..8ce46c1 100644
--- a/daemon/fw/strategy.cpp
+++ b/daemon/fw/strategy.cpp
@@ -6,6 +6,7 @@
 
 #include "strategy.hpp"
 #include "forwarder.hpp"
+#include "core/logger.hpp"
 
 namespace nfd {
 namespace fw {