software/slapos-testing: use [test] to install erp5.util

now we have a test extra

software/slapos-testing/software.cfg

@@ -74,8 +74,7 @@ setup = ${slapcache-repository:location}
 
 [erp5.util-setup]
 <= setup-develop-egg
-# XXX erp5.util does not have `test` extra require, but has a `testnode` extra require with same dependencies
-egg = erp5.util[testnode]
+egg = erp5.util[test]
 setup = ${erp5.util-repository:location}
 depends = ${slapos.core-setup:egg}