properly set the FilesystemBackend parameters when using NFS

Change-Id: Ie4a00ebbb760738bcae11a527c671ee7f715313e
Bug-Url: https://bugzilla.redhat.com/1125244
Signed-off-by: Jiri Moskovcak <jmoskovc@redhat.com>
(cherry picked from commit 7aa85ae9eb80302a1d6c4c063030961e485761e4)