Add support for NetApp direct drivers

netapp_wsdl_url is only valid for the regular drivers.
netapp_storage_service is optional for all NetApp drivers.
See here for example:
http://docs.openstack.org/grizzly/openstack-block-storage/admin/content/netapp-iscsi-driver-direct-7mode.html

Change-Id: I8c6cd9d63b3e6da683bf210f1b4db7bd7fd3d315
Merge "Add support for NetApp direct drivers"