For adding tag, allow filtering on buildrequires to find out koji_tags from tag inheritance
The original AddTagHandler.get_match_tags_in_inheritance finding out module's
koji_tags added to tag inheritance should also allow filtering modules on
buildrequires.
On the other hand, this method is duplicated with existing method
find_module_tags_from_koji_inheritance. So the solution is to promote
find_module_tags_from_koji_inheritance to BaseHandler and be reusable for both
of the handlers.
Signed-off-by: Chenxiong Qi <cqi@redhat.com>