virttest: Update qemu_io to use get_qemu_io_binary to get qemu_io_cmd

Use get_qemu_io_binary provide by utils_misc in qemu_io to ignore some
structure change problem from now on.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
Merge pull request #1642 from ypu/qemu_io

virttest: Update qemu_io to use get_qemu_io_binary to get qemu_io_cmd