Correct opt type for nexenta_chunksize/blocksize
Correct opt type for nexenta_chunksize/blocksize

When defined as a string with an integer default value, configuration
generation fails. Set to IntOpt based on help description and 4K/16K
values.

Change-Id: Ifaa92e15e3af837d87f71190702e66245c0fe7df

openstack/cinder,dims/cinder,Hybrid-Cloud/cinder,Datera/cinder,Nexenta/cinder,NetApp/cinder,eharney/cinder,openstack/cinder,j-griffith/cinder,phenoxim/cinder,Datera/cinder,ge0rgi/cinder,j-griffith/cinder,dims/cinder,bswartz/cinder,phenoxim/cinder,eharney/cinder,Nexenta/cinder,mahak/cinder,bswartz/cinder,cloudbase/cinder,NetApp/cinder,cloudbase/cinder,Hybrid-Cloud/cinder,mahak/cinder