Fix HDFS url description, and other various edits

HDFS url description is wrong as a result of code changes. This was
the major motivation for this CR.

Additional changes

* formatted for 80 characters
* consistent use of '.' at the end of bullets
* added mention of Spark
* adding '.sahara' suffix is no longer necessary
* some other minor changes

Closes-Bug: 1376457
Change-Id: I72134bcdf6c42911d07e65952a9a56331d896699
(cherry picked from commit a718ec7ddf85ef2e1e17868f6e2cd05b1c2762cd)