Relative path reference to an image in core causing all CI tests failing since 2015-09-17. See T112968
From jquery.wikibase.toolbarbutton module
.wikibase-toolbarbutton-disabled .ui-icon { background-image: url(../../../../../../../../resources/lib/jquery.ui/themes/smoothness/images/ui-icons_888888_256x240.png); }
See jenkins log at https://integration.wikimedia.org/ci/job/mwext-testextension-zend/8951/console