Add explanatory in-line comment regarding single vs double quotes for sshpass

It was fixed in 8624b6dcb311635679969392672fb31b272c9581. And since the
Salt coding style is to use single quotes it makes sense to explain in
the code why this needs to be the way it is.
Fix typos
Merge pull request #8316 from holmboe/pylint-and-comments

In-line comments and typos