support cube-specific db and coll in mongo2 backend
support cube-specific db and coll in mongo2 backend

pombredanne/cubes,jell0720/cubes,cesarmarinhorj/cubes,pombredanne/cubes,noyeitan/cubes,she11c0de/cubes,jell0720/cubes,cesarmarinhorj/cubes,she11c0de/cubes,jell0720/cubes,noyeitan/cubes,zejn/cubes,ubreddy/cubes,ubreddy/cubes,pombredanne/cubes,ubreddy/cubes,zejn/cubes,she11c0de/cubes,zejn/cubes,cesarmarinhorj/cubes,noyeitan/cubes