patchtest: improve test issue messages

patchtest: improve test issue messages

The patchtest tests provide vague feedback to the user, and many of them
also provide redundant 'fix' strings that could easily be incorporated
into the issue messages themselves. Simplify them so that it is more
clear what the errors are and how they can be addressed. No
recommendation is given when the issue string adequately conveys the
issue, e.g. with a missing "LICENSE" entry in a newly-created recipe.

Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>