KNL-1212 Fix paging for SiteService.getSites().

We were doing paging on selecting the site IDs and then when we loaded the uncached sites from the DB we were doing paging again on these results which lead to no results being found on the second page of results.

git-svn-id: https://source.sakaiproject.org/svn/kernel/trunk@307548 66ffb92e-73f9-0310-93c1-f5514f145a0a