Due to vars precedence rules, included vars during role runtime can
be overriden only with extra-vars, meaning that defined group/host_vars
will be ignored.
This would fix the usage of group_vars while should work for other
usecases.
Though, `defaults_from` should be supplied explicitly while importing
the role.
Change-Id: I6a213aeaecff87c7e74507c0c2fed9b54c10f908
efbf1454c6