libvirt: Fix cleanup
libvirt: Fix cleanup

Finally fix cleanup procedure. Start docker compose without any passed
env - cleanup will be skipped. Add LIBVIRT_CLEANUP=something before
docker-compose up - cleanup will run.

Mirantis/virtlet,vefimova/virtlet,vefimova/virtlet,nhlfr/virtlet,vefimova/virtlet,nhlfr/virtlet,nhlfr/virtlet,Mirantis/virtlet,nhlfr/virtlet,vefimova/virtlet