Since we want to start including this class conditionally, detect cases
where packagegroup files use the old ordering and inform the user they
need to update this.
(From OE-Core rev: 30aaada4b79fc1acad5fdaba98071b63c52b9e05)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
9541ec7b55