[CI] libvirt-gitlab-executor project is now part of the libvirt namespace

This is just a small announcement that the $subj project which was created in order to provision customized VMs as throwaway worker nodes for our functional test suite utilizing GitLab's custom executor feature was transferred to the libvirt's GitLab namespace. Anything that relates to both infrastructure and executing the functional test suite in a customized environment should go to this project. Regards, Erik