function bytesToUuid(buf, offset) {
  var i = offset || 0;
  var bth = byteToHex;
  return  bth[buf[i++]] + bth[buf[i++]] +
          bth[buf[i++]] + bth[buf[i++]] + '-' +
          bth[buf[i++]] + bth[buf[i++]] + '-' +
          bth[buf[i++]] + bth[buf[i++]] + '-' +
          bth[buf[i++]] + bth[buf[i++]] + '-' +
          bth[buf[i++]] + bth[buf[i++]] +
          bth[buf[i++]] + bth[buf[i++]] +
          bth[buf[i++]] + bth[buf[i++]];
}
Convert array of 16 byte values to UUID string format of the form:
XXXXXXXX-XXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX