MXS-1929: Take ResultSet into use

Replaced the previous RESULTSET with the new implementation. As the new
ResultSet doesn't have a JSON streaming capability, the MaxInfo JSON
interface has been removed. This should not be a big problem as the REST
API offers the same information in a more secure and structured way.

server/core/internal/server.hh

@@ -18,4 +18,4 @@
 
 #include <maxscale/resultset.hh>
 
-ResultSet* serverGetList();
+std::unique_ptr<ResultSet> serverGetList();