Mover should move the file blocks to default storage once policy is unset

HDFS-9534 added new API in FileSystem to unset the storage policy. Once policy is unset blocks should move back to the default storage policy.

Currently mover is not moving file blocks which have zero storage ID

      // currently we ignore files with unspecified storage policy
      if (policyId == HdfsConstants.BLOCK_STORAGE_POLICY_ID_UNSPECIFIED) {
        return;
      }