Revert "logical: Only raw volumes are supported"
    
    This reverts commit 6682d6219d4595b51f06867e0c30e7efd745f682.
    
    The "if (vol->target.format != VIR_STORAGE_FILE_RAW)" check in the
    createVol backend. This check is bogus because virStorageVolDefParseXML()
    in conf/storage_conf.c sets target.format only if volOptions in
    virStoragePoolTypeInfo has formatFromString set, and that's not the
    case the logical backend.
    
    So the check always fails and breaks volume creation.