Fix description for "Barbarism of editting a file"

Fix description for "Barbarism of editting a file"

There are some barbarism located in the file cinder/HACKING.rst.
  line11 and line21 : there is no full point at the end of a sentence.
  line14 and line23 : after a sentence, there are two space between
  the full point and the first letter of the second sentence.
I think the correct format of the above question as blow.
   - [N319] Validate that debug level logs are not translated.
   - [C302] six.text_type should be used instead of unicode.
   - [N325] str() and unicode() cannot be used on
   an exception. Remove or use six.text_type().
   - [C304] Enforce no use of LOG.audit
   messages. LOG.info should be used instead.

Change-Id: I2896bacc5379786ed115d47e520bf5bc2af0028a
Closes-Bug: #1487665