Add qemu-* command test cases

The qemu-* commands are explicitly unsupported in RHEL products, so
the testing strategy is mainly focus on return status and libvirtd status after
command been executed.

This depends on PR:
https://github.com/autotest/virt-test/pull/1666
Do you have any plan to test other agent command, for example, `guest-fsfreeze-*`, `guest-fstrim` `guest-ping`