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/tests/test-common.hpp b/tests/test-common.hpp
index 8095431..c65d1c2 100644
--- a/tests/test-common.hpp
+++ b/tests/test-common.hpp
@@ -9,6 +9,7 @@
 
 #include <boost/test/unit_test.hpp>
 #include "core/global-io.hpp"
+#include "core/logger.hpp"
 #include <ndn-cpp-dev/security/key-chain.hpp>
 
 namespace nfd {