Add a package QA check for wether any of the variables used by
features_check.bbclass is set while not inheriting the class itself.
(From OE-Core rev: c06489d102682504afe33f9fee3facd9628b3f57)
Signed-off-by: Jacob Kroon <jacob.kroon@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>