NFS drivers don't honor vm size with volume from an image

The bug has been encountered with the NFS generic driver
(cinder.volume.nfs.NfsDriver) and the NetApp NFS driver
(cinder.volume.drivers.netapp.nfs.NetAppDirectCmodeNfsDriver). I believe
that drivers based on distributed filesystem such as GlusterFS, nexenta
and scality are also impacted however I didn't test it those backends.
However since most of them already inherit from the RemoteFsDriver
class, this should be fine.

Change-Id: I14575da69a2c99c7cbcece27b40a171153371ee3
Fixes: bug #1183459
Merge "NFS drivers don't honor vm size with volume from an image"