src: Refactoring common.hpp and minimizing exposed includes

Face class has relatively large rewrite to hide internals using
Implementor pattern.  As of this commit, <boost/asio.hpp> is not
automatically included whenever ndn-cxx/face.hpp is included.  If it is
needed to directly work with io_service, asio.hpp should be specifically
included.

Change-Id: Ie742b851025b4e3da634eb981319df0f42937855
diff --git a/tests-integrated/security/test-validator-config.cpp b/tests-integrated/security/test-validator-config.cpp
index e122523..def5ae3 100644
--- a/tests-integrated/security/test-validator-config.cpp
+++ b/tests-integrated/security/test-validator-config.cpp
@@ -16,6 +16,9 @@
 
 #include "security/key-chain.hpp"
 #include "util/io.hpp"
+#include "util/scheduler.hpp"
+
+#include <boost/asio.hpp>
 
 #include "boost-test.hpp"