NexentaStor4 iSCSI: convert blocksize to str
NexentaStor4 iSCSI: convert blocksize to str

Blocksize option was changed to IntOpt for proper config
generation, converting it to str before sending request.

Change-Id: I4a60580fb227428b3754ab7bc0c7aa2ffe1b6443

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