[test] Import "cubicweb_link" instead of "cubes.link"

Following up on "new style" changes so that class names comparison
works.

test/unittest_link.py

@@ -2,7 +2,7 @@
 from cubicweb.devtools.testlib import CubicWebTC
 from cubicweb.web.views import uicfg, actions
 
-from cubes.link import views
+from cubicweb_link import views
 
 afs = uicfg.autoform_section