add new named errors
add new named errors

phoenix-io/openstorage,kunalkushwaha/openstorage,libopenstorage/openstorage,ModelRocket/openstorage,libopenstorage/openstorage,jvinod/ost,pault84/openstorage,pault84/openstorage,libopenstorage/openstorage,ModelRocket/openstorage,pault84/openstorage