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

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