tests: resetGlobalIoService for every test

All tests must use BaseFixture or a fixture derived from it to get this feature.

This commit also fixes a few warnings in tests/mgmt, and moves test cases into nfd::tests namespace.

refs #1290

Change-Id: I891441a5abce170e35648d463f7157b18429f79f
diff --git a/daemon/table/fib-nexthop.hpp b/daemon/table/fib-nexthop.hpp
index 41c121b..4dc2b65 100644
--- a/daemon/table/fib-nexthop.hpp
+++ b/daemon/table/fib-nexthop.hpp
@@ -29,14 +29,14 @@
   getFace() const;
   
   void
-  setCost(int32_t cost);
+  setCost(uint32_t cost);
   
-  int32_t
+  uint32_t
   getCost() const;
 
 private:
   shared_ptr<Face> m_face;
-  int32_t m_cost;
+  uint32_t m_cost;
 };
 
 } // namespace fib