duplicate chapter - hdfs bootstrap

[camypaj]

Hi Steve,

thanks for this book, it's just what I needed :)
I'm working on a pull request, but this seems more like a "issue", since this block (HDFS Boostrap)
seems identical to the one a few paragraphs above:

1. NN reads in a keytab and initializes itself from there (i.e. no need to kinit; ticket
   renewal handed by UGI).
2. Generates a Secret

Delegation tokens in the NN are persisted to the edit log, the operations OP_GET_DELEGATION_TOKEN
OP_RENEW_DELEGATION_TOKEN and OP_CANCEL_DELEGATION_TOKEN covering the actions. This ensures
that on failover, the tokens are still valid

Also it seems to contain a typo in the title that I've just noticed.
"Boostrap" -> "Bootstrap".

Cheers,
Camypaj