qemu's process maybe reaped by other goroutine reaper

[lifupan]

Some programs using this vendor may have their own children reapers which has reaped the
qemu's process before cmd.Wait to reap it. For this case, the cmd.Run/cmd.Wait
will get an error contains substring of "no child processes", thus it's needed
to ignore this error and deal it as success.

[fidencio]

Closing this one as it's been fixed by: kata-containers/runtime#1004