PYTHON-2459 Implement unified GridFS tests (#1012)

Author: ShaneHarvey

.evergreen/resync-specs.sh

@@ -108,6 +108,9 @@ do
     csot|CSOT|client-side-operations-timeout)
       cpjson client-side-operations-timeout/tests csot
       ;;
+    gridfs)
+      cpjson gridfs/tests gridfs
+      ;;
     load-balancers|load_balancer)
       cpjson load-balancers/tests load_balancer
       ;;