utils/checkpackagelib: CommentsMenusPackagesOrder: change the type of variable 'level'

utils/checkpackagelib: CommentsMenusPackagesOrder: change the type of variable 'level'

Change the type of variable "level" to make it a class member.
It will be used not only locally.

Signed-off-by: Jerzy Grzegorek <jerzy.m.grzegorek@gmail.com>
Cc: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Reviewed-by: Ricardo Martincoski <ricardo.martincoski@gmail.com>
[Thomas: initialize self.level in the before() method, as suggested by
Ricardo]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>