Serialize the CI

Building Deimos takes up too many resources to run two build jobs at the same time. Therefore I added new stages for the CentOS 7 and 8 build respectively, disabling the Authorisation build because that is rather unimportant anyway.

Changelog:
* Separate test CI stages for CentOS 7 and 8
* Disable 'Authorisation Disabled' test
5 jobs for serialize_ci in 25 minutes and 33 seconds (queued for 3 seconds)