Change hostgroup_service relations

Change expected output of one unit test and add another
test for clarification purposes.

service "production_service" is applied to "production_servers"
and therefore it does not make sense that get_effective_hostgroups()
also returns "prod_and_dev" hostgroup.

In the same manner, getting effective services for prod_and_dev should
only return services that are applied to all hosts in that hostgroup.

Issue #115