Fixed few UI tests - minor changes

- updated the referenced manifest_url names under common/manifests.py. The properties file contains 
`manifest.key_url` instead of `main.manifest.key_url`. Similar change for fake_url.
- updated bz id for failed arch test and added wait_for_ajax for usergroup test
You need to update you local properties as the previous configuration path was right according to what is proposed on the sample properties file (for more info https://github.com/SatelliteQE/robottelo/blob/master/robottelo.properties.sample#L21)