fw: refactor Strategy registry

Strategy registry is moved into Strategy class.
Strategy instantiation logic is implemented in Strategy::create.
These are in preparation of supporting Strategy parameters.

refs #3868

Change-Id: If36a08ad25a00a7008a5eccc8cfe4f6c63638676
diff --git a/tests/daemon/fw/best-route-strategy2.t.cpp b/tests/daemon/fw/best-route-strategy2.t.cpp
index ec6e951..b8406b5 100644
--- a/tests/daemon/fw/best-route-strategy2.t.cpp
+++ b/tests/daemon/fw/best-route-strategy2.t.cpp
@@ -73,6 +73,11 @@
 
 BOOST_FIXTURE_TEST_SUITE(TestBestRouteStrategy2, BestRouteStrategy2Fixture)
 
+BOOST_AUTO_TEST_CASE(Registration)
+{
+  BOOST_CHECK_EQUAL(Strategy::listRegistered().count(BestRouteStrategy2::STRATEGY_NAME), 1);
+}
+
 BOOST_AUTO_TEST_CASE(Forward)
 {
   fib::Entry& fibEntry = *fib.insert(Name()).first;