Remove the insignificant_tests CONFIG option in favor of a BLACKLIST
file. The test blacklisted have been found using CI builds logs.
Change-Id: Iac07316862cff9b5085dacdf9f35e691cff09384
Task-number: QTBUG-27571
Reviewed-by: Janne Anttila <janne.anttila@digia.com>
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@theqtcompany.com>
