Use namespace std in place

This commit uses std in place in header files rather than
using namespace.

Signed-off-by: Priyanga Ramasamy <priyanga24@in.ibm.com>
Change-Id: If8e77ad0d23c7e6d8f16ea93e65f34aefb6b157f
diff --git a/test/vpd-manager-test/reader_test.hpp b/test/vpd-manager-test/reader_test.hpp
index 85d458f..b108df2 100644
--- a/test/vpd-manager-test/reader_test.hpp
+++ b/test/vpd-manager-test/reader_test.hpp
@@ -10,6 +10,7 @@
 {
   public:
     MOCK_METHOD(std::string, readBusProperty,
-                (const string& obj, const string& inf, const string& prop),
+                (const std::string& obj, const std::string& inf,
+                 const std::string& prop),
                 (override));
 };