Improve help strings

Several changes to make help strings consistent:
* End options with "."
* Add missing space between lines
* Capitalize first word of help strings
* Improve wording of text
* Make strings consistent.
* Use "VPN service"

Closes-Bug: #1321871

Change-Id: I8fdc356574d680c222b8a26dcc5ad8e3a2b4e4f1
Merge "Improve help strings"