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
@yumingfei It's used in vcpucount case, but with little difference, vcpucount did setvcpus operation while here only handle ga setting.