NFS fixups

- Move fsal_rgw config to ceph-common, as it's shaered with ceph-rgw
- Update all.docker.sample with NFS config
- Rename fsal_rgw to nfs_obj_gw and fsal_ceph to nfs_file_gw, because
  the former names mean nothing to non-Ganesha developers

Signed-off-by: Daniel Gryniewicz <dang@redhat.com>