Improve help strings

Follow oslo.config style guide for help strings better to create
consistent help strings:
* Finish help strings with "."
* Add missing spaces between words

Change-Id: I6191842c253b254768bcc5c22fcfb435296f3945
Co-Authored-By: Shilla Saebi<shilla.saebi@gmail.com>
Merge "Improve help strings"