Some small update for qemu related code

This pullreq include some small update for qemu related code in the following items:

1. several error context update for cases
   This error context update will not influence the functionality of the case. They are some improve from the feed back of our manual test guys. And with Qingtang's idea of [RFC] Bug report generating script, we may can make the job analyse more automatic in the future.

2. Some interface update as 64 -> x86_64 we find during the merge

3. Some update for cfg files

4. A bug fix for a mistake I made during the push

So far, in this round the cases should be all pushed out except cgroup(yunzheng is handling it and it should coming soon).

And we have some complex ones that need more time and work on them, such as unattened_install to make sure they will not ruin virt-test. So we split them to another task. :)

I will have another round check after all the cases is in next to make sure that there is nothing missing.

Thanks a lot for everyone helps to reviewing and pushing the cases. :)