Prefer man directly over groff

[kevin-sellers]

groff is great, as it easily generates ASCII text for help pages, but lacks the escape sequences of man pages (bold, italic, etc.). Since it's evident that aws help pages are formatted in the same way as manual pages, I would expect it to look and feel the same way. For this reason, instead of piping output through groff and then the user's pager of choice, we now favor man (when available) to format these pages in the standard way (which automatically uses the correct pager).

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.