qemu: Add new test check_unhalt_vcpu

(1) Use qemu-img to create an unbootable image.
(2) Start vm with the image created by step 1.
(3) Use ps get qemu-kvm process %cpu, if greater
    than 90%, report fail.

Signed-off-by: Qingtang Zhou <qzhou@redhat.com>
Signed-off-by: Yiqiao Pu <ypu@redhat.com>
Signed-off-by: Suqin Huang <shuang@redhat.com>
Signed-off-by: sshang <sshang@redhat.com>