Expand libvirt test driver API coverage

The libvirt library provides a stable API for managing platform virtualization utilizing different hypervisors or virtual machine monitors. Each hypervisor requires its own driver inside libvirt, but not all API functions are supported by all drivers or hypervisors yet. In addition to the standard drivers, there is a supplementary fake driver, called test driver, designed to let applications test against libvirt with fake data and not have any effect on the host. As of today, there are still a lot of API functions not implemented by the test driver. The goal of this project is to expand the API coverage of the test libvirt driver.