Implement Location header for session auth

From the redfish specification 1.5.0, page 98:
"""
The response to the POST request to create a session shall include the
following:
...
A Location header that contains a hyperlink to the newly created session
resource
"""

This implements the location header properly, per specification.

Tested by:
Attempting POST on the Sessions resource, and observing a "Location"
header be set.

Change-Id: Ia62c385bedf67e6267d573771b04a211ba332f21
Signed-off-by: Ed Tanous <ed.tanous@intel.com>
diff --git a/redfish-core/lib/redfish_sessions.hpp b/redfish-core/lib/redfish_sessions.hpp
index a32a660..ca1c375 100644
--- a/redfish-core/lib/redfish_sessions.hpp
+++ b/redfish-core/lib/redfish_sessions.hpp
@@ -167,6 +167,9 @@
             username);
     res.addHeader("X-Auth-Token", session->sessionToken);
 
+    res.addHeader("Location",
+                  "/redfish/v1/SessionService/Sessions/" + session->uniqueId);
+
     // Return data for created session
     memberSession.doGet(res, req, {session->uniqueId});