By implementing this method we will decrease dependency
on SERVICE_NAMES. python-tempestconf loops over any
service which has a class implementation under
config_tempest/services directory. Therefore we can easily
set service availability in the loop by calling
set_availability method which sets appropriate values in
[service_available] section of tempest.conf.
This review also fixes the problem with not taking
service's versions into account when setting service
availability.
Story: 2002787
Task: 29632
Change-Id: Ica42fe6ae57eaef6bffd28b557f6b178a2ed8fb9
33e39f3606