Port NetApp NFS drivers to use ABC driver model

NetApp NFS drivers inherit from NfsDriver, which in turn
inherits from RemoteFSDriver.  Now that RemoteFSDriver and
NfsDriver have been ported to the ABC driver model, we have ported
the NetApp NFS drivers as well.

Change-Id: I785d0bb282589cab9efee60ab7900e09d54bb7e0
Partially-implements: blueprint abc-driver-update

cinder/volume/drivers/netapp/dataontap/nfs_base.py

@@ -39,6 +39,7 @@ from cinder import exception
 from cinder.i18n import _, _LE, _LI, _LW
 from cinder.image import image_utils
 from cinder import utils
+from cinder.volume import driver
 from cinder.volume.drivers.netapp import options as na_opts
 from cinder.volume.drivers.netapp import utils as na_utils
 from cinder.volume.drivers import nfs
@@ -50,7 +51,11 @@ CONF = cfg.CONF
 
 
 @six.add_metaclass(utils.TraceWrapperWithABCMetaclass)
-class NetAppNfsDriver(nfs.NfsDriver):
+class NetAppNfsDriver(driver.ManageableVD,
+                      driver.CloneableVD,
+                      driver.CloneableImageVD,
+                      driver.SnapshotVD,
+                      nfs.NfsDriver):
     """Base class for NetApp NFS driver for Data ONTAP."""
 
     # do not increment this as it may be used in volume type definitions