Test to check if the activation-key's content-host limit actually limits its usage

I realised we were assigning the server_name from the conf file for every test. I am not sure what would be the best/correct solution for it, but I am suggesting we need to review this approach. IF we are able to fix this in this PR it's great, else we can track this in another issue as I do understand that it does take time to look into it. :)

For now may be we can try this:
Under SetUp() function of ActivationKey:
ActivationKey.server_name = conf.properties['main.server.hostname']

and then in tests s/server_name/self.server_name/