EZP-22973: Fix test PHP warnings with postgres - 

Related: https://jira.ez.no/browse/EZP-22973

This is a followup on #986, should "fix" the `PHP: Deprecated: mysql_escape_string() `... warning that is visible when running tests in travis with postgres.

The problem is that `eZCollaborationItemTest` extends `ezpDatabaseTestCase` but is missing `setUp()`; In addition creating a eZUser mock caused this warning because test providers are executed in first place; refactor creation to actual test function.