tests: use BOOST_TEST_CONTEXT and BOOST_DATA_TEST_CASE where possible

Fix the last two "CanBePrefix unset" warnings in unit tests

Change-Id: Ifd2420ae98e7c4741a1c20e7fa0d52f74d7178c8
diff --git a/tests/unit/unit-tests-pch.hpp b/tests/unit/unit-tests-pch.hpp
index dd67e02..f3cfdf2 100644
--- a/tests/unit/unit-tests-pch.hpp
+++ b/tests/unit/unit-tests-pch.hpp
@@ -32,4 +32,6 @@
 
 #include "tests/key-chain-fixture.hpp"
 
+#include <boost/test/data/test_case.hpp>
+
 #endif // NDN_CXX_TESTS_UNIT_UNIT_TESTS_PCH_HPP